Musnad Ahmad 30:1462

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from Muhammad ibn Ishaq, from al-Zuhri, from Sa‘id, from Abu Hurayrah: "When the news of the death of the Negus reached the Prophet, may Allah bless him and grant him peace, he prayed over him, and they lined up behind him, and he pronounced four takbirs over him."