The Islamic community is divided into two main branches: Shiism and Sunniism. 

One of the significant differences between these groups lies in the concept of “Imamate”. Imamate is a religious doctrine embraced by Shiite Muslims, which asserts that after the holy Prophet (PBUH & HP), Allah almighty did not leave his servants without guidance. According to Shiite belief, the holy Prophet (PBUH & HP) designated successors who would guide the people, interpret the verses of the Quran and propagate the teachings of Islam. The number of these successors are 12 and they all are the descendants of the Messenger (PBUH & HP). The hadiths of the Prophet (PBUH & HP), accepted by all Muslims for their authenticity, confirm the existence of these successors.

Twelve successors 

According to a hadith narrated by Sunni recorders the Prophet (PBUH & HP) stated:

Indeed, this religion will not end until twelve successors [of me] rise among the people. 

The narrator says that after that, the Prophet said something that he didn’t hear so he asked his father what did the Messenger say and his father replied: “the Prophet said that they all are from Quraysh, the tribe of the Prophet. (1)

The holy Prophet (PBUH & HP) also said:

Indeed, I leave you two kinds of successor: one is the Book of Allah (The Quran) and the other one is my household. And indeed, they do not depart from each other until they meet me near the Kother pool [on the Judgement Day]. (2)

These reliable hadiths clearly show that the successors of the Prophet (PBUH & HP) are twelve men from his family.

The names of the twelve Imams on a tablet

There is a hadith narrated by the Shiite hadith recorders that mentions the names of all these successors. This hadith provides valuable insights into the Shiite Imams. 

Imam Sadiq (AS), the sixth Shiite Imam, narrates that his father, Imam Baqir (AS), once asked Jabir ibn Abdullah al-Ansari (one of the Prophet’s most important companions) to recount the story of the tablet he had seen in the hands of Lady Fatimah (AS), the beloved daughter of the Messenger, and tell him about the things that was written on that tablet. 

Jabir said “I swear to Allah, once during the Prophet’s lifetime, I visited the house of lady Fatimah (AS) to congratulate her on the birth of her son, Hussain (AS). Then I saw a green tablet on her hands, which I assumed to be made of emerald and it had white text resembling the light of the sun. So, I asked her what it was and she replied, ‘This is a tablet that Allah has bestowed upon my father, containing the names of my father, my husband, my sons and the successors of my father who are my descendants. The Messenger gave it to me to cheer me up.’” 

Jabir further added, “Your mother gave it to me, and I read it and copied it on another tablet.” Imam Baqir (AS) then asked “Can you show me your copy?” and Jabir replied “Yes.” 

The text was as follows:

In the name of Allah, the most Compassionate, the most Merciful.

This is a writing from Allah, the Almighty, the Wise, to Muhammad (PBUH & HP), His Prophet, His Light, His Messenger, His Mediator and the Guide to Him. The Trustable Spirit [Gabriel] has brought it from the Lord of the people. 

O Muhammad! Respect my names and be thankful of my gifts and do not deny my favors. Indeed I am Allah and there’s no deity but me. I am the annihilator of the oppressors and the helper of the oppressed and I am the Judge of the Judgement Day. So I punish the ones who desire the kindness of the others or dread the justice of others with a punishment I punish no one alike. Then worship only me and trust only on me. 

Indeed, I sent no Prophet whose time came to end except that I chose someone as their successor and I made you better than all the prophets and made your successor better than all the successors. And kindly gave you your two grandsons: Hassan (AS) and Hussain (AS). 

Then I chose Hassan as the repository of my knowledge after his father [Imam Ali (AS)] and I chose Hussain as the source of my revelations and made him a great one by giving him martyrdom and I made his destiny with salvation then he is the noblest martyr and the highest-ranked among all martyrs… 

Afterward, Allah almighty proceeds to mention all the successors of the Prophet (PBUH & HP) in this lengthy text as follows:

Ali (AS) the son of Imam Huassain (AS), also known as Sajjad, Muhammad al-Baqir, Jafar as-Sadiq, Musa al-Kazim, Ali ar-Ridha, Muhammad al-Javad, Ali al-Hadi, Hassan al-Askari. And the last of them is Imam Mahdi (AS), the savor of all Muslims. (3) He is still alive and will appear again in the future alongside Jesus, establishing justice on Earth full after it has been plagued by tyranny and oppression. (4)

All Shias believe that these twelve men are the successors of the Prophet and after the Prophet (PBUH & HP) they all came and taught people the teachings of Islam but the last of them is now alive and unknown by people. All Muslims, whether Shiite or Sunni, share the belief that Imam Mahdi (AS) will eventually emerge as the ruler of all the entire Earth, bringing justice to prevail. The Holy Quran says:

Certainly, We wrote in the Psalms, after the Torah: ‘Indeed My righteous servants shall inherit the earth.’ (21:105)

Resources 

1. Sahih al-Muslim, Muslim an-Neishaburi, vol.3, pg.1452
2. Musnad Ahamd, Ahmad ibn Hanbal, vol.35, pg.512
3.  Al-Kafi, Sheikh Koleini, vol.1, pg.528
4.  Al-Kafi, Sheikh Koleini, vol.1, pg.338
    

Let's start our topic with a question. What is the meaning of 'special' in your life? What days have been special to you, your family, or even to your community? The answer may vary from mere personal occasions like birthdays, anniversaries, etc. to more public ones such as New Year's Eve, Easters, or any National Day. The same is true about every religion, culture, or society. Different days of the year have different meanings in every religious community; such as Laylatul Qadr for Muslims. 

Everything that the Almighty God has created is Noble

 "(He) Who perfected everything which He created" (Quran 32:7) 

 "…So whichever way you turn, there is the face of Allah! Allah is indeed all-bounteous, all-knowing." Quran (2:115)

"There is nothing in existence but beauty, for God created the cosmos only in His image, that is, in the image of His infinite beauty." Ibn Arabi [i], [1]& [2].

This does not, however, mean that all creatures are the same! Can river stones be equal to those of precious pearls in the oceans? The world is the world of differences, and that actually makes it delightful and adventurous. This is also manifested in people's different languages and colors, which is a sign of Allah's balanced and sophisticated creation.  

"And of His signs is … the diversity of your languages and your colors. Indeed in that are signs for those of knowledge" (Quran 30:22)

If every stone were like a pearl would have the pearl had the same value that it has now? How about the days of the year? God is indeed in All Days, but again this is God's plan for us to value specific days or nights more than others. The Islamic Holy scripture refers to a night that has the value as equal to a thousand months, called Laylatul Qadr, the Night of Decree. Likewise, the month of Ramadan or that of Dhul Hijja has special significance in Islam during which distinct rituals and etiquettes are prescribed for Muslims.  What is it that really makes them unique? For that, we will have to take a look at Islamic resources. 

Which Days or Nights Are Superior in Islam?

As indicated earlier, certain nights and days are adored in Islamic culture.

In a week, Friday does not only mark the weekend, but it has a special meaning for Muslims. The Surah "al-Juma" in the Quran declares the importance of the Friday prayer that is a congregational prayer held at Friday noon, and it is also referred to as the "the pilgrimage of the poor" in Islamic traditions. 'Forgiveness of sins,' 'reduction of the difficulties in the Day of Judgment,' and 'great rewards for every step to the place of the Friday prayer' are only a scratch over the surface of the benefits of this ritual for those who attend it [3]. 

In a year, the three months of Rajab, Shaban, and Ramadan are highly appreciated. It is narrated that Prophet Muhammad (PBUH&HP) has said: "Indeed Rajab is the month of Allah, while Shaban is my month and Ramadan is the month of my community" [4]. Ramadan is the month in which the Quran was revealed to the Prophet (PBUH&HP). It is also the month of fasting for Muslims [5]. 

In a grand tradition, the Prophet (PBUH&HP) narrates that Allah (SWT) said: "Fasting is for me, and I am the one who rewards for it" [6], "The gates of the fire are closed (in this month), so ask your Lord not to open them and Satans are in chains. So ask your Lord not to dominate them over you." This month is the best month in the sight of Allah, its days are the best, its nights are the best nights and its hours are the best hours… your breath in it (the month of Ramadan) is glorification (of God), and your sleep in it is worship" [7].

The Night of Decree (Laylatul Qadr) 

Moreover, it is in this month that the Night of Decree (Laylatul Qadr) is celebrated. A night that is regarded as equal to a thousand months, and it is when humankind's destiny is decreed for the coming year. It was on this night that the Holy Quran was revealed to the Prophet [8]. Indeed, Ramadan is the best month, and the Night of Qadr (Decree) is its heart. Believers stay awake the entire night and pray for blessings and forgiveness. It is the holiest night of the year, and it would be unwise to be heedless of the tremendous benefits of this night. It is a grand opportunity that God has gifted us with; there is a night that our whole year is decreed and if praying that night, we can ask Him to bless us with a year full of the happiness, the spirituality, the health and the success and whatever good we want in our lives. That's how God gives us the chance to rebuild our destiny, and a new beginning of our spiritual calendars, to ask forgiveness for the sins we have committed in the past year while praying for a better fate in the coming year.

The above briefly indicates how some days, months, and nights are special in Islam. The question now remains how we are going to use them and benefit from them.  When we are invited to such a special feast undoubtedly, we have to get prepared and plan for it; otherwise, we gain nothing but regret.

That's the beauty of having faith. Your days and nights are not equal. Each and every one of them has their own distinct meanings. It makes the spiritual journey of a servant sweeter and more enjoyable. He/she has always something to do to get closer to His Lord.

Notes:

[i] An Arab Andalusian Muslim scholar, mystic, poet, and philosopher, whose works have grown to be very influential. 

References:

1.  Claude Addas, The Experience and Doctrine of Love in Ibn Arab, http://www.ibnarabisociety.org/addas1.html 
2. William C. Chittick, The Divine Roots of Human Love,
3. divine roots
4.  Al-'Allama al-Majlisi, Bihar al-Anwar, vol. 86, p. 197, Al-Shaykh al-Saduq, Man la yahduruh al-faqih, vol. 1, p. 427, Nuri, 
5.  Al-'Allama al-Majlisi, Bihar al-Anwar, vol. 104, p. 123.
6. The Quran 2:183&5
7. Shaykh al-Hurr al-Amili, Wasā'il al-Shi'ah, vol. 10, p.400.
8. Al-Shaykh al-Saduq, Al-Amāli, p.95.
9. The Quran, Chapter 97th.