Musnad Ahmad 1760

Abdullah bin Ja"far said: If you could have seen me with Qutham and ‘Ubaidullah, the two sons of "Abbas, when we were boys, playing. The Prophet (ﷺ) passed by on a mount and said: “Lift this one up to me.” He seated me in front of him, and he said to Qutham: "Lift this one up to me.” And he put him behind him. "Ubaidullah was dearer to ‘Abbas than Qutham, but he did not feel embarrassed in front of his uncle to carry Qutham and leave him. He said: Then he patted my head three times and said each time: "O Allah, take care of Ja"far"s children for him [after he is gone].” He [the narrator] said: I said to ‘Abdullah: What happened to Qutham? He said: He was martyred. I said: Allah and His Messenger know best where good lies. He said: Yes indeed