When Muhammad died in 632, his will as to who should lead the community after his death was not clearly and legally established. Lying on his death-bed, he had asked for writing-material: "Bring ink and paper so that I may lay down in writing for you that which will always guard you from error." But 'Umar said: "The pain is confusing him, we have God's Book; this is sufficient." Thus his companions quarrelled at his death-bed as to whether they should fetch the writing-material, and Muhammad sent them away. As the 'Qur'an' contains no ruling about who was to succeed him, the Prophet's father-in-law, Abu-Bakr, was chosen to be the first Caliph at the instigation of the mighty 'Umar during a stormy community gathering. From the beginning protests were raised by influential Muslims against this way of bestowing the Caliphate and it was recalled that Muhammad had on different occasions publicly designated his cousin and son-in-law 'Ali as his successor. According to tradition, on the way back from his last pilgrimage to Mecca the Prophet had stopped the caravan by the water-hole of Khumm and had a platform erected out of saddles on which 'Ali had to sit. Muhammad had then addressed his people: "Whoever has me as a master has 'Ali as a master". He announced his approaching end and spoke of the two treasures which he was leaving behind for them: "The greatest treasure is the Book of God... Hold fast unto it, do not relax its laws or falsify it! The other treasure is the line of my successors." (126:2)

According to the Shiah interpretation, the Caliphate was usurped by Abu-Bakr and 'Umar and taken away from the real chosen ones, the descendants of the Prophet. With the exception of 'Ali who was Caliph from A.D. 656 to the year he was murdered, 661, Muhammad's descendants were excluded from the Caliphate and exposed to violent persecutions by the ruling dynasties. However, the Shiah have never ceased to claim that the Caliphate is a hereditary office and belongs to the natural descendants of the Prophet. According to the so-called Shiah Twelvers (the state religion of Persia since 1572), twelve descendants of Muhammad exercised their office as "Imam", an office which apart from 'Ali's five years as Caliph lacked all worldly power and was therefore a vestige of what it should have been. (126:3)

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