‘Ali ra was, in Sunni tradition, to be the fourth and last of the righteous Caliphs. Shi’ite Islam, however, acknowledges twelve Imams and they are considered perhaps not yet infallible, but their words and traditions are considered part of compulsory religious law:
1. ‘Ali ibn Abi Talib (600–661), also known as ‘Ali, Amir al-Mu’minin
2. Hasan ibn ‘Ali (625–669), also known as Hasan al-Mujtaba
3. Husayn ibn ‘Ali (626–680), also known as Husayn al-Shahid, also known as Sah Hüseyin
4. ‘Ali ibn Husayn (658–713), also known as ‘Ali Zayn al-Abidin
5. Muhammad ibn ‘Ali (676–743), also known as Muhammad al-Baqir
6. Jafar ibn Muhammad (703–765), also known as Jafar al-Sadiq
7. Musa ibn Jafar (745–799), also known as Musa al-Kazim
8. ‘Ali ibn Musa (765–818), also known as ‘Ali al-Raza
9. Muhammad ibn ‘Ali (810–835), also known as Muhammad al-Jawad (Muhammad at-Taqi), also known as Taki
10. ‘Ali ibn Muhamad (827–868), also known as ‘Ali al-Hadi, also known as Naki
11. Hasan ibn Ali (846–874), also known as Hasan al-Askari
12. Muhammad ibn Hasan (868- ), also known as al-Hujjat ibn al-Hasan, also known as Mahdi; believed to be hidden by Allah (Occultation).
Fatimah ra also Fatimah al-Zahraa daughter of Muhammed (615–632), is seen as infallible in Shiism, and as the leader of all women in Paradise.
‘Ali ra has been respectfully recorded by Sunni sources, but Shi’ites preserved a lot more words and actions, as another source of ahadith on ‘Ali. Not all of those are accepted by Sunni community. The best known Shi’ite hadith collections are the four books and Nahj al Balagha.
The four books are:
1 Kitab al Kafi by Mohammad Ya’cub Kulayni (death 950 AD), again divided into Usul al Kafi, Furu al Kafi and Rawdat al Kafi.
2 Man la yahduruhu al Faqih by Sheikh Saduq
3 Tahdhib al Ahkam by Abu Ja’far al Tusi
4 Al Istibsar by Abu Ja’far al Tusi
Furu al Kafi is considered the most authoritative Shia hadith collection and concerns details of religious law. Usul al Kafi, by many scholars considered as weak or fabricated, concerns the principles of religion and Rawdat al Kafi concerns various religious aspects including some writings of the Imams. Sheikh Al Kulayni was born in the village of Kulayn near Tehran, but later moved to and worked in Baghdad as chief of the Shia scholars in jurisprudence during the ‘Abbasid Caliph Al Muqtadir. Sheikh Al Kulayni was a contemporary of the four successive special representatives and ambassadors of the legendary hidden twelfth Imam Muhammad ibn Hasan. His year of death is debated to be 940 or 941 AD. Sunni scholar Ibn Hajar has written appreciative words on this prominent Shi’ite scholar and he is considered one of the main and most trusted experts on ahadith in the Shi’ite community.
Man la yahduruhu al Faqih is a hadith collection compiled by the famous Iranian Shia hadith scholar Abu Ja’far Muhammad ibn ‘Ali ibn Babawaih al Qummi, better known as Ibn Babawaih or Al Sheikh al Saduq. Abu Ja’far, Al Sheikh al Saduq, lived in what was considered the golden age of Shia Islam, 703-765 AD, and worked mainly in his own country Iran, where he was considered one of the main and most trusted scholars, by Sunni as well as Shia Muslims, in the city of Qom, Iran’s main centre for Islamic studies. Abu Ja’far is believed to be the sixth infallible Imam of Shi’ite Islam. His succession led to a schism in Shia Islam: Abu Ja’far is the last Imam to be both recognized by Twelver and Ismaili Shi’tes. Abu Ja’far was more than a theologian; he was a polymath with vast knowledge on astronomy, physics, medical and other natural sciences. Abu Ja’far has been recorded as a teacher of Sunnite Hanafy Maddhab’s founder Abu Hanifa.
Tahdhib al Ahkam (‘The Refinement of the Laws in Terms of the Explanation of the Sufficiency’) is written by the founder of the religious seminary in Najaf, Abu Ja’far al Tusi (d. 1067 AD), the city where caliph ‘Ali was killed, city that had become a pilgrim centre for Shi’ite Islam and grew to be the leading centre, even today, of Shi’ite scholarship since Abu Ja’far al Tusi’s arrival. Abu Ja’far al Tusi had to leave Baghdad for Najaf after religious turmoil and violence, which was also focused against his person and possessions. Many Sunni and Shia ‘ulema’ were killed or had to leave Baghdad in a climate increasingly hostile towards Shi’ites. Al Tusi’s work concerns practical regulations for carrying out the shariah considering the great differences that had arisen in Shia traditions. It deals with topics as ritual cleansing for salat; hunting and ritual slaughter; marriage and divorce; manumission of slaves. Sheikh Al Tusi died in Najaf and his grave is, also today, a much frequented place of visit.
The fourth main book of Shia ahadith is Al-Istibsar, also written by Sheikh Al Tusi, and is a more popular summary of the main issues of jurisprudence for beginners, and a reminder.
Nahj al Balagha
The perhaps most famous collection of Shia traditions is Nahj al Balagha (Peak of Eloquence): The words, sermons and letters by the first Shi’ite Imam, ‘Ali ibn Abi Talib, the Prophet’s son in law and nephew. The collection was recorded by Al Sharif al Radi in the 10th century. Sheikh Al Radi is a said to be a direct descendant of the main Shi’ite Imams, and thus of the Prophet. The Shia don’t include this work in their Hadith books. Most Sunni scholars do not regard the book as an authentic work; prominent scholars as Ibn Taymiyyah and Yusuf an Nabhani warned Sunnis against this work, because of its hostile tone towards the companions of the Prophet saws.
For a better understanding of Islamic early history, and therefore its legitimacy, it is impossible to ignore the schools of thought that rose in an early stage. Moreover, at the highest academic level, scholars of the different schools of thought did communicate and even followed each other’s classes. A third group I'd like to mention now, is the Ibadi movement, one of the earliest schools, descending from the group of Kharijites or Khawarij, which is seen as notorious among the Islamic mainstream.