The Hadith al-Thaqalayn refers to a saying (hadith) about al-Thaqalayn, which translates to "the two heavy things." In this hadith Prophet Muhammad referred to the Qur'an and Ahl al-Bayt ('people of the house', Muhammed's family) as the two heavy things. Although the Hadith is accepted by both Sunnis and Shi'as, the two groups differ on the exact wording of what Muhammad said, as well how to interpret these words. The Shias use the Hadith al-Thaqalayn to prove their claim that Muhammad said that Imam Ali is the next successor. (Ahl al-Bayt). The Sunnis reject that Prophet muhammad said Imam Ali is the next successor.
Sunni and Shi'a Concordance
Both Sunnis and Shi'as accept that Muhammad said the following:
"I m leaving among you something which is very important and should be followed, you will not go astray if you get hold of it after I am gone, one part of it being more important than the other: Allah's Book, which is a rope stretched from Heaven to Earth, and my close relatives, who belong to my household. These two will not separate from one another till they come down to the reservoir, so consider how you act regarding them after my departure." (Tirmidhi, Sahih Muslim)
Both Sunnis and the Shi'a believe in respecting . However, it is only the Shi'a who claim that the Caliph (leader) is Imam Ali after Prophet Muhammad as he said on the land of Kaum. Sunnis reject the claim that prophet Muhammad said "Ali is the next successor after me".
The Shi'as believe that Muhammad said Hadith al-Thaqalayn multiple times in multiple settings in multiple wordings. They argue that Muhammad said Hadith al-Thaqalayn at Mount Arafat during his Farewell Sermon, at Ghadir Khumm, in the mosque of Medinah, during his last illness, and at many other places and times. The Shi'as believe that Muhammad said this hadith so many times because he wanted to stress how important it was that the Muslims only take his own descendants as leaders.
The Shi'as believe that this hadith is , meaning that it has been related so many times by so many people that there is no doubt about its authenticity. The Shi'a claim that this hadith is the most authentic of hadiths, claiming that it has been narrated by over 35 companions of Muhammad.
The Hadith al-Thaqalayn is used by the Shi'a, among other reasons, to justify their claim of 's . Shi'as view this hadith as a clear indication that Muhammad wished to keep the matter of leadership within his own family, starting with his cousin Ali. They say that Muhammad was clearly indicating that only the Ahl al-Bayt have a right to authority and leadership. It is based on this claim that the Shi'as reject the first three Sunni Caliphs, referring to them as usurpers and tyrants.
Because the Shi'a believe that Muhammad said Hadith al-Thaqalayn on many occasions, the Shi'a have many different versions of what Muhammad said. One such version corresponds closely to what the Sunnis also believe in:
Muhammad said: "One of them (i.e. the Thaqalayn) is the Book of Allah and the other one is my select progeny (Itrat), that is family (Ahlul-Bayt). Beware of how you behave (with) them when I am gone from amongst you, for Allah, the Merciful, has informed me that these two (i.e., Quran and Ahlul-Bayt) shall never separate from each other until they reach me in Heaven at the Pool (of al-Kawthar). I remind you, in the name of Allah, about my Ahlul-Bayt. I remind you, in the name of Allah, about my Ahlul-Bayt. Once more! I remind you, in the name of Allah, about my Ahlul-Bayt."
The Shi'as, however, also believe in other versions of the Hadith such as:
"I have left with you something, which if you strictly adhere to, you shall never go astray–The Book of Allah and my progeny."
"I leave you two weighty things, if you stick to both you will never go astray after me: the Book of Allah and my progeny."
"I am leaving for you two precious and weighty Symbols that if you adhere to both of them, you shall not go astray after me. They are, the Book of Allah, and my progeny, that is, my Ahl al-Bayt. The Merciful has informed me that these two shall not separate from each other till they come to me by the Pool (of Paradise)."
It is these latter versions that more strongly support the Shi'a interpretation that Muhammad intended to keep the leadership of the Muslims within his own family.
The Sunnis reject the idea that the Hadith al-Thaqalayn is , and they also reject the idea that it was narrated by over 35 of Muhammad's companions. Instead, the Sunnis reject many of the versions of Hadith al-Thaqalayn, classifying them as Dhaeef, or weak in authenticity, and believe that it was narrated by no more than 10 of Muhammad's companions.
They believe that Muhammad only mentioned Hadith al-Thaqalayn at Ghadir Khumm, and reject the idea that Muhammad said it during his Farewell Sermon atop Mount Arafat. The Sunnis believe that Muhammad only mentioned the Two Weighty Things on his way back to Medinah (at Ghadir Khumm), and that his speech was therefore directed primarily to those living in Medinah because it was they who would have the task of taking care of Muhammad's family after his death.