Musnad Ahmad 33:1175

Yazid ibn Harun narrated to us, Qatadah informed us, from Ata ibn Abi Rabah, from Jabir ibn Abdullah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Pray for a brother of yours who has died in a land other than yours." They said: "Who, O Messenger of Allah?" He said: "The Negus, Sahmah." He [the narrator] said: So I said: "Did you stand in rows for him?" He said: "Yes, I was in the third row."