Imam JAAFAR BIN MOHAMMAD (ASWS), from his FATHER (ASWS), from his grandfather (Imam HUSAIN (ASWS)), from the MESSENGER OF ALLAH (SAWW), who said:
On the night of Me’raaj when I reached Sidratul Montaha, I was told:
O MOHAMMAD (SAWW)! Appoint ALI (ASWS), who is the best (one to be) your successor. ALI (ASWS) is the master of the Muslims, Imam of the pious, and the leader of the companions of Paradise on the Day of Judgement.”
(Amaali of Tousi 1:196, Amaali Al-Mufid 173.)