Sahih Muslim Book 9, Hadith Number 3601.

Chapter: It is forbidden for a slave to take anyone as his ally except one who emancipates him.

Ibrahim al-Taimi reported on the authority of his father: ‘Ali b. Abu Talib (Allah be pleased with him) addressed us and said: He who thinks that we (the members of the Prophet’s family) read anything else besides the Book of Allah and this Sahifa (and he said that Sahifa was tied to the scabbard of the sword) tells a lie. (This Sahifa) contains (problems) pertaining to the ages of the camels and (the recompense) of the injuries, and it also records the words of the Prophet (may peace be upon him): Medina is a sacred territory from ‘Ayr to Thaur (it is most probably Uhud). He who innovates (an act or practice) or gives protection to an innovator, there is a curse of Allah and that of His angels and that of the whole humanity upon him. Allah will not accept from him (as a recompense) any obligatory act or supererogatory act, and the responsibility of the Muslims is a joint responsibility; even the lowest in rank can undertake the responsibility (on behalf of others), and he who claims anyone else as his father besides his own father or makes one his ally other than the one (who freed him), there is a curse of Allah, that of His angels and that of the whole mankind upon him. Allah will not accept the obligatory act of the supererogatory act (as a recompense) from him.