Kulaini, Ibn Babawayh and Shaykh Tabarsi etc. have narrated through authentic chains of narrators from Imam Ja’far Sadiq (a.s.) that His Eminence, Ja’far returned from Habasha and reached the Prophet on the day of the conquest of Khyber. The Messenger of Allah (S) was highly elated and he said: “I can’t say on which to express more happiness: on the conquest of Khyber or the return of Ja’far.”
When Ja’far arrived, the Prophet embraced him and accorded him a warm welcome and asked: “Do you want me to bestow you something?” “Yes, O Messenger of Allah (S).” People thought that the Holy Prophet (S) would give him a lot of wealth from the booty of Khyber and they craned their necks to see what he was giving. The Holy Prophet (S) said to Ja’far: I give you something and teach you an act which if you perform everyday, it will be better than everything in the world.
Or even if you perform it once a month or once a year, all sins committed during this time will be forgiven.” Then the Messenger of Allah (S) taught him a prayer called Prayer of Ja’far at-Tayyar.