Abu Tamim al-Jayshani says: I heard Sayyiduna Amr bin al-As (may Allah be pleased with him) saying: One of the Companions of the Prophet (peace and blessings be upon him) told me that the Prophet (peace and blessings be upon him) said: "Indeed, Allah Almighty has granted you an additional prayer, so offer it between Isha and the morning prayer: it is the witr, it is the witr." Behold! That narrator was Sayyiduna Abu Basrah al-Ghifari (may Allah be pleased with him). Abu Tamim says: Once Sayyiduna Abu Dharr al-Ghifari (may Allah be pleased with him) and I were sitting. Sayyiduna Abu Dharr al-Ghifari (may Allah be pleased with him) took hold of my hand, and we walked to Sayyiduna Abu Basrah (may Allah be pleased with him), and we found him at the door next to the door of Sayyiduna Amr (may Allah be pleased with him). Sayyiduna Abu Dharr al-Ghifari (may Allah be pleased with him) said: O Abu Basrah, did you hear the Prophet (peace and blessings be upon him) saying: "Indeed, Allah Almighty has granted you an additional prayer, so offer it between Isha and the morning prayer: it is the witr, it is the witr"? Sayyiduna Abu Basrah (may Allah be pleased with him) replied: Yes. Sayyiduna Abu Dharr al-Ghifari (may Allah be pleased with him) asked: Did you yourself hear this from the tongue of the Prophet (peace and blessings be upon him)? He replied: Yes.
Ahmad and al-Tabarani in al-Mu'jam al-Kabir recorded it. Ahmad recorded it with two chains, one of which has narrators who are the narrators of the Sahih, except Ahmad's teacher Ali bin Ishaq al-Sulami, who is nonetheless thiqah (trustworthy).