Hadith of the thaqalayn

The hadith of the thaqalayn (حديث الثقلين) refers to a statement, attributed to the Islamic prophet Muhammad, that introduces the Quran, the principal religious text in Islam, and his progeny as the only two sources of divine guidance after his death. Widely reported by both Shia and Sunni authorities, the hadith of the thaqalayn is of particular significance in Twelver Shia, where their Twelve Imams are viewed as the spiritual and political successors of Muhammad.

Hadith of the thaqalayn
There exist several versions of this hadith in Sunni sources. The version that appears in the Musnad Ahmad ibn Hanbal, a canonical Sunni hadith collection, reads, "I [Muhammad] left among you two treasures which, if you cling to them, you shall not be led into error after me. One of them is greater than the other: The book of God (Quran), which is a rope stretched from Heaven to Earth, and [the second one is] my progeny, my Ahl al-Bayt. These two shall not be parted until they return to the pool [of abundance in paradise, kawthar."

Muhammad might have repeated this statement on multiple occasions, including his Farewell Pilgrimage and later at the Ghadir Khumm, shortly before he died in 632. The version of this hadith in Al-Sunan al-kubra, another Sunni hadith collection, adds the warning, "Be careful how you treat the two [treasures] after me." Similar versions of the hadith can be found in other major Sunni sources, including Sahih Muslim, Sahih al-Tirmidhi, and Sunan al-Darimi. According to the Twelver Shi'a theologian Muhammad Husayn Tabataba'i, the hadith of the thaqalayn has been transmitted through more than a hundred channels by over thirty-five Companions of the Prophet.

Shia Islam limits the Ahl al-Bayt to the Ahl al-Kisa, namely, Muhammad, his daughter Fatima, her husband Ali, and their two sons, Hasan and Husayn. In Shia theology works, the Ahl al-Bayt often also includes the remaining Shia imams. There are various interpretations in Sunni Islam, though a typical compromise is to include Muhammad's wives in the Ahl al-Bayt, in addition to the Ahl al-Kisa. In some Sunni versions of the hadith, however, ahl al-bayt has been replaced with sunna; that is, practices of Muhammad.

Significance in Sunni Islam
Some Sunni versions of the hadith of the thaqalayn replace with sunna, that is, practices of Muhammad. This change is either intended to challenge the Shia implications of the hadith, or, if authentic, may imply that the of Muhammad are a source of his sunna. Muhammad is indeed viewed as the 'living Quran', the embodiment of God's will in his behavior and words. Both Sunni and Shia Muslims uphold the Quran and the sunna of Muhammad, though Shia extends the sunna to also include the traditions and practices of their imams.

Significance in Twelver Shi'ism
In Twelver Shi'ism, the hadith of the thaqalayn establishes a parallel between the Quran and the family of Muhammad, implying that the two serve as the only sources of divine guidance after Muhammad. The hadith also implicitly describes (some) descendants of Muhammad as the true interpreters of the Quran, and those descendants are viewed as the living embodiments of the Quran in Twelver Shi'ism. As divine guides, those descendants must also be infallible lest they lead their followers astray. The hadith also implies that Earth is never void of a descendant of Muhammad, an infallible imam, who serves as the divine guide of humankind in his time. These are the Twelve Imams in Twelver Shi'ism. The last of these imams, Muhammad al-Mahdi, is believed to remain miraculously in occultation since 874 and is expected to return in the end of times to eradicate injustice and evil.

The belief in the mahdi remains popular among all Muslims, possibly owing to numerous traditions to this effect in canonical Sunni and Shia sources.