Musnad Ahmad 30:2535

Yahya narrated to us, from Malik, who said: Al-Zuhri narrated to me, from Sa'id ibn al-Musayyib, from Abu Hurayrah, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) announced to us the death of the Negus on the day he died. He went out to the prayer ground (musalla), lined up his companions behind him, and pronounced four takbirs over him."