In different cultures or religions, people pay special attention to some specific numbers. For example, numbers 7, 40, and 70 are amongst lucky numbers, and number 13 is known to be a cursed number in some cultures. However, the significance of the number 40 among many cultures and religions is very noticeable. Therefore, this question may arise that what is so special about this number? Can number forty bring luck and happiness to people? Is it a fact or just a superstition? Let’s have a quick look at the background of the number forty in different religions.

Number Forty in Christianity 

Number forty has been mentioned in the Bible in different verses:

1- Jesus (PBUH) fasted "forty days and forty nights" in the Judean desert. (Matthew 4:2, Mark 1:13, Luke 4:2).

2- Forty days was the period from the resurrection of Jesus to the ascension of Jesus (PBUH). (Acts 1:3).

3- Rain fell for "forty days and forty nights" during the Flood (Genesis 7:4). [1] 

Number Forty in Islam 

Number forty is mentioned in the Quran four times: 

1 & 2- Prophet Moses (PBUH) spent 40 days on Mount Sinai, where he received the ten commandments (2: 51, 7: 142).

3- Prophet Moses (PBUH) and his people were lost in the desert for forty years. (5: 26)

4- As mentioned in the Quran, It seems that the age of forty should be the time when a human being is supposed to reach his/her intellectual perfection and understanding of life. This is the time when one can plan the rest of his/her life in a way to gain the most from this world for the hereafter:

“… When he comes of age and reaches forty years, he says, ‘My Lord! Inspire me to give thanks for Your blessing with which You have blessed my parents and me, and that I may do righteous deeds which please You, and invest my descendants with righteousness. Indeed I have turned to you in penitence, and I am one of the Muslims.” (46: 15) 

It is narrated from Prophet Muhammad (PBUH & HP) that “When one becomes forty years old, Allah tells his two guardian angels, ‘From now on, be strict on him and note every small and big deed he does’” [2]. The narration emphasizes that the age of forty shapes the personality of a person, and if he/she is still unable to manage his/her life, it is his/her fault for having wasted his/her life in the wrong way. 

Number Forty in Narrations and the Conduct of Scholars

There are so many narrations from Prophet Muhammad (PBUH & HP) that mention number forty. Here we list a few of these narrations:

1- “He who purifies his faith for Allah for forty days, Allah will flow the springs of wisdom from his heart to his tongue” [3].

 2- “The prayers of the one who drinks wine are not accepted for forty days unless he repents” [4] [i].

 3- “The prayers of a person who gossips would not be accepted for forty days and nights” [5].

Some scholars say that number forty is used to emphasize the significant amount of something.

4- “One who leaves his house to gain a gate of knowledge by which he deviates the wrong towards righteous, or deviance to guidance, his deed is equal to forty years worship of a worshipper” [6].

The Fortieth Day after Burial (Arba’een)

In some cultures, it is a tradition that forty days after a passed-away person’s burial, close relatives and friends gather in a place with the family of the late person and remember the passed-away person and wish peace and patience for his/her family. In this manner, they show the family of the deceased person that they are not alone, and people will help them and support them when required. 

It is based on this tradition, taken from the conduct of the Prophet (PBUH & HP) and his Progeny (AS) that Muslims travel to Karbala on the 40th (Arba’een) martyrdom commemoration of Imam Hussain (AS) and his companions; Not only to sympathize with the household of Prophet (PBUH & HP) on this event, but to show their gratefulness for their courage in preserving the true Islam and the conduct of the Prophet (PBUH & HP). More importantly, Muslims show that the aim of Imam Hussain (AS) is still observed and taken care of. 

Is It OK to Follow the Rules Related to Number Forty? 

Based on the importance that some verses of the Quran and narrations of the Prophet (PBUH & HP) give to number forty, Muslim scholars, especially those who are fond of Islamic mysticism and self-purification, pay special attention to number forty in their conducts and life-style. 

Therefore, there is nothing wrong with trying to benefit from the blessings that the number forty may have. And it is trustworthy because Allah and the Prophet (PBUH & HP) have mentioned it. However, normal human beings do not have a real knowledge of numbers and the wisdom behind them. 

A Logical Interpretation 

As mentioned in a narration earlier, the Prophet (PBUH & HP) says that if you purify your faith for forty days, you will see a great result. [7] The reason is that if one works so hard on his/her spirituality to be able to purify his faith for forty days, it will become a habit for him. Allah says in the Quran, “Be wary of Allah, and Allah will teach you, and Allah has knowledge of all things” (2: 282), which is very much relevant to the mentioned narration. Therefore, one interpretation of doing something for forty days is that whatever you do for this long period, with persistence, will become your habit, and after something becomes a habit, you can easily go on with it for the rest of your life.

Conclusion 

To sum up, there is no such thing as lucky or cursed numbers. And instead of trying to find luck in numbers, one should work hard to develop his personality, spirituality, knowledge, and wisdom. 

But the reason number forty has been mentioned by the Prophet (PBUH & HP), and Islamic scholars might be a symbol of enormousness, meaning that if you persist in doing something for a considerable amount of time, it will become your habit. However, the reason why they insisted on number forty might be because they wanted to spread unique conduct and a specific discipline among the believers. 

Notes:

[i] Some may think that if praying and fasting are not accepted for forty days after drinking, then it will be OK if they do not pray or fast for forty days after they drink. It should be noted that praying and fasting are still compulsory for the person who drinks. However, the sin is counted so huge that they should repent from it, deciding not to commit it again, and say their prayers and perform fasting and other obligations.

References 

1. number in religion
    Al-kafi, Vol 8, P. 108
    Bihar al-Anwar, vol. 67, p. 242
    Mustadrak al-Wasa’il, vol. 17. P. 57
   Al-Kafi, Vol. 6, p. 400
    Amali- e Tousi, p. 118
   Bihar al-Anwar, vol. 67, p. 242
2.  

Life is a journey full of twists and turns. Without a guide in this deceptive path, one can become lost, forfeiting something that cannot be regained - the precious gift of redemption. That is why Islam emphasizes the need for Muslims to never be without a leader. Prophet Mohammad (PBUH&HP) is the best example of a Muslim within Islam.

There has certainly been for you in the Messenger of Allah an excellent pattern for anyone whose hope is in Allah and the Last Day and [who] remembers Allah often. (The Holy Quran 33:21)

O you who have faith! Obey Allah and His Apostle, and do not turn away from him while you hear [him]. (The Holy Quran 8:20)

These Quranic verses firmly establish that no one surpasses Prophet (PBUH&HP) as the ideal role model, guiding us to emulate his actions and lifestyle for our salvation. When we follow someone as a model in our life, we inherently respect his beliefs and ideas. 

From this, we deduce that if our model is devoted to Islam, religion, and the path of Allah's pleasure, we will also try to align ourselves with that path and potentially attain spiritual ascension. Our model here is not an ordinary person but our dear Prophet. Therefore, there is no disputing the goodwill of this revered figure. An important thing that we must learn from the Prophet (PBUH&HP) as the supreme model for Muslims is to know whom to love and whom to dislike.

The question is: how does understanding Prophet’s feelings towards individuals would help us? 
The answer lies in this: “By following the Prophet as an example, we can accurately discern these people, subsequently progressing toward Allah’s satisfaction and eternal happiness.” 

Two figures whom the Prophet constantly favored were Imam Hassan and Imam Hussein (as). Imam Hussein (AS) was born on the third of Sha'ban in the fourth year of AH.

Since the great Prophet passing in the tenth year of AH, Imam Hassan and Imam Hussein (AS) spent their childhood with their dear grandfather.

Before delving further, let us know more about our third Imam. Imam Hussein (as) is also called Aba-Abdillah and Sayyid al-Shuhada among the Shias. He is the third Imam for the Shias, martyred in the course of Ashura. He is the second child of Imam Ali (AS) and Fatemeh Zahra (AS), and the grandson of Prophet Mohammad (PBUH&HP). Following his brother Imam Hassan’s (AS) leadership, he took charge of leading the Shias for ten years. Both Shia and Sunni historical records confirm that the Prophet of Islam (PBUH&HP) announced his martyrdom at his birth and chose the name "Hussein" for him. (1)

The Prophet held deep affection for Imam Hassan and Imam Hussein and recommended everyone to love them. Imam Hussein (AS) is one of the of Prophet’s Ahl al-Bayt and also one of the recipients of the verse of purification*.

Numerous narrations from Prophet Mohammad (PBUH&HP) extol Imam Hussain’s virtue. A famous narration quotes the Prophet (PBUH&HP) on Imam Hussain (AS): “Hussain is from me and I am from Hussain. Allah loves who loves Hussain.” (2)

Through this narration, the Holy Prophet (PBUH&HP) show other Muslims the sacred position of Imam Hussein (PBUH) and imparts the exceptional stature of this lineage. In an era where falsehood and hypocrisy infiltrate the Muslim community, this saying compels believers to rid themselves of hypocrisy and misguidance. 

Regrettably, despite its resonance, this profound message did not deter the brutal martyrdom of Sayyid al-Shuhada (PBUH), which transpired in the Karbala before thousands of seemingly Muslim individuals.

The Prophet’s (PBUH&HP) adoration for Imam Hussein (AS) served a dual purpose: it conveyed not only his love for his grandson, but also aimed to engender affection towards Imam Hussein as the Imam of the Ummah, rallying people to follow him. Therefore, the Holy Prophet of Islam consistently introduced the Imam Ali, Fatima Zahra, Imam Hassan and Imam Hussein (AS) as his family and Ahl al-Bayt. He equated them with the Quran on numerous occasions,  underscoring the necessity for Muslims to accept their leadership and guidance for spiritual elevation. The Prophet also said this in the hadith of the thaqalayn: 

"Indeed, I am leaving two things among you, to which if you hold yourself, you will never astray: the book of Allah –who is almighty and great- and my Ahl al-Bayt (household), my 'itra (family). O people hear! And I have announced to you that indeed you will enter my presence and I will ask you about what you did to the thaqalayn (two weighty things) and the thaqalayn are the book of Allah and my Ahl al-Bayt."(3)

Conclusion: 

These narrations illuminate Imam Hussein’s (AS) lofty status in the the Prophet’s (PBUH&HP)eyes and the Prophet’s responses to him serves as a guide. Not only are Muslims, as followers of the Holy Prophet, must praise and love Imam Hussein, but we must also adopt his behavior, thoughts, and ethics, and follow his path in our lives. Furthermore, the Prophet's interactions with Imam Hussein underscore that those who harbor hostility or animosity towards him today are not true Muslims. This group should not be regarded as part  of the Prophet’s (PBUH&HP) religion.

References:

1.  Al‑Irshad (2nd Volume - page 130)
2.  Sunan al-Termizi (6th volume – number 3775)
3.  Al-Kafi (1st Volume – page 452)

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*The Verse of Purification is the 33rd verse of Al-Aḥzāb in the Quran (33:33). The verse has special importance for Shia Muslims due to giving information about Ahl al-Bayt of Prophet Muhammad (PBUH&HP). Shias reportedly believe it to designate the "Ahl al-Bayt" being infallible.