Sayyiduna Abu al-Yusr (may Allah be pleased with him) narrates: I was sitting with the Prophet (peace and blessings be upon him) when Abu Amir al-Ash'ari came to him and said: "You had sent me on such-and-such a task. I came to Mu'tah; the people there were drawn up in ranks. Sayyiduna Ja'far (may Allah be pleased with him) mounted his horse, put on his armour, took the banner, and walked until he came to the enemy, and said: 'Who will deliver this to the one it belongs to?' One of those present said: 'I will.' He sent it with him. Then he advanced and struck with his sword until he was killed." Tears flowed from the eyes of the Prophet (peace and blessings be upon him). The Prophet (peace and blessings be upon him) led us in the Zuhr prayer, then went inside and did not speak with us at all. Then the iqamah was called for the prayer, and he came out and led us in the Asr prayer, and did not speak with us at all. He did the same at the Maghrib and Isha prayers: he would go inside and not speak with us, although whenever he finished a prayer he used to turn his face towards us. Then the Prophet (peace and blessings be upon him) came out for the Fajr prayer at his usual time, the time at which he used to come out before. At that time Abu Amir al-Ash'ari and I were sitting. The Prophet (peace and blessings be upon him) sat down between us and said: "Shall I not tell you about a dream that I saw? I entered Paradise and saw Ja'far with two wings soaked in blood, and Zayd was opposite him, and Ibn Rawahah was with them, looking as though he had turned his face away. I will tell you about that: when Ja'far advanced and saw that he would be killed, he did not turn his face away; Zayd did likewise; but Ibn Rawahah turned his face away."
Al-Tabarani recorded it. Its chain contains a narrator, Thabit bin Dinar Abu Hamzah, who is da'if (weak).