Hadith 21: The Condition of Honor

Imam Sadiq (as) said: Whoever wants to be in the neighborhood of the Prophet (pbuh&HP) and next to Ali (AS) and Fatima (AS) should not leave the pilgrimage of Imam Hussain (AS).  
Wasa'il al-Shi'ah, vol. 10, p. 331, p. 39

Hadith 22: Pilgrimage, Divine Duty

Imam Sadiq (as) said: If one of you observes the Ihram of Hajj for the entire of his life but does not visit Imam Hussain (as), he has left the right of the Messenger of Allah (PBUH&HP) because the right of Hussain (as) is a divine duty and obligatory for every Muslim.
 Wasa'il al-Shi'ah, vol. 10, p. 333

Hadith 23: Karbala, the Kaaba of Perfection

Imam Sadiq (as) said: Whoever does not visit the grave of Imam Hussain (as) until he dies, his faith will be incomplete and his religion will be incomplete, and when he goes to heaven, he will be lower than the believers there. 
Wasa'il al-Shi'ah, vol. 10, p. .335

Hadith 24: From Pilgrimage to Martyrdom

Imam Sadiq (as) said: Do not leave the pilgrimage of Imam Hussain (as) and recommend it to your friends and companions as well! May Allah prolong your life, increase your sustenance, and may Allah bless you alive and you will not die except as a martyr. 
Wasa'il al-Shi'ah  vol. 10, p. 335

Hadith 25: The Hadith of Love

It was narrated from Imam Sadiq (as) that he said: Whoever Allah wants good, will put the love of Hussain (AS) and his pilgrimage in his heart, and whoever Allah wants bad, will have him hate Hussain (AS) and anxious with his pilgrimage.
 Wasa'il al-Shi'ah  vol. 10, p. 388, Sea of Lights, vol. 98, p. 76

Hadith 26: A Sign of Being a Shiite

Imam Sadiq (as) said: Whoever does not visit the grave of Imam Hussain and dies as our Shiite and dies, is not our Shiite, and even if he is from the people of Paradise, he is the guest of the people of Paradise.
Kamel Al-Ziyarat, p. 193, Bihar Al-Anwar, vol. 98, p.4

Hadith 27: Ascension Platform

Imam Sadiq (as) said: Whoever visits the grave of Hussain (as) and has knowledge of the right of that Imam, Allah Almighty will register him in the highest rank.
Man la yahzurul Faqih, vol. 2, p.581

Hadith 28: The School of Knowledge

Imam Musa Kadhim (as) said: The least reward that is given to the pilgrim of Imam Hussain (as) on the banks of the Euphrates is that all his sins, before and after, are forgiven. Provided that he knows the right, honor and guardianship of that Imam.
Mustadrak al-Wasa'il, vol. 10, p. 236, quoting Kamil al-Ziyarat, p. 138

Hadith 29: Like the Pilgrimage of Allah

Imam Reza (as) said: Whoever visits the grave of Imam Hussain (as) on the banks of the Euphrates is like the one who has visited Allah. 
Mustadrak al-Wasa'il, vol. 10, p. 250, quoting in full

Chapter Three: Ashura and Arbaeen

Hadith 30: Pilgrimage at Ashura

Imam Sadiq (as) said: Whoever visits Imam Hussain (as) on the day of Ashura, heaven will be obligatory for him. 
Iqbal al-A'mal, p. 568

Hadith 31: Above Prosperity

Imam Sadiq (as) said: Whoever wakes up on the night of Ashura next to the shrine of Imam Hussain (as), on the Day of Judgment he will rush to Allah stained in his blood, like someone who was killed in Karbala next to Imam Hussain (as). 
Wasaelu shiah, vol. 10, p.372

Hadith 32: Signs of Faith

Imam Hassan Askari (as) said: The signs of a believer are five: 

1 Fifty prayers 

2 Arbaeen pilgrimage

3 Ring in the right hand 

4 Prostrating on the ground 

5 Saying loudly the name of Allah, (Bismillah Rahman Rahim)

 Wasaelu shia, vol. 10, p. 373, and also Al-Tahdhib, vol. 6, p. 52

Chapter Four: Torbat and Tasbih of Love

Hadith 33: His Porch 

The Prophet of Islam (PBUH&HP) said: Know that the answer to prayer is under the dome of his shrine and healing is in his soil, and the Imams (as) are of his children.
 Mustadrak al-Wasa'il, vol. 10, p.335

Hadith 34: Soil and Training

Imam Sadiq (as) said: Take your children with the soil of Hussain (as) (Karbala) because the soil of Karbala insures your children. 
Wasaelu Shiah, vol. 10, p.410

Hadith 35: The Greatest Medicine

Imam Sadiq (as) said: The cure for any pain is in the soil (torbat) of Hussain (as) and it is the greatest medicine. Kamil Al-Ziyarat, p. 275 and Wasa'il al-Shi'ah, vol. 10, p. 410

Hadith 36: Torbat (soil of Karbala) and seven hijabs

Imam Sadiq (as) said: Prostration on the soil of Hussain (as) tears the seven veils. 
Mesbah al-Muttahid, p. 511, and Bihar al-Anwar, vol. 98, p. 135

Hadith 37: Prostration on the Soil of Love

Imam Sadiq (as) did not prostrate on the ground except on the soil of Hussain (as) and he did this in violence for the sake of Allah.
Wasailu shiah vol. 3, p.608

Hadith 38: Rosary with the Soil of Karbala

Imam Sadiq (as) said: Prostration on the soil of Karbala can light up to the seventh earth, and whoever has a rosary from the soil of the shrine of Hussain (as) with him, is a truthful person, even if he says nothing.
Man la yahzurulFaqih vol 1 p 268 

Hadith 39: Healing Soil

Imam Kadhim (as) while narrating a hadith announcing his death, said: do not take anything from the soil of my grave to seek blessings, because it is forbidden for us to eat any soil except the soil of my grandfather Hussain (as), Allah Almighty has healed only the soil of Karbala for the Shiites and our friends. 
Jami ahadith, vol. 12, p.533

Hadith 40: One of the Four Needs

Imam Musa ibn Ja'far (as) said: Our needs are four things:

1. Prayer mat on which prayers are offered.

2. Rings on the finger

3. Toothbrush with which to brush teeth

4. A rosary from the shrine of Imam Hussain (as) Tahdhib al-Ahkam, vol. 6, p. 75
 

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