Sayyiduna Hanzalah bin al-Rabi' al-Katib (may Allah be pleased with him) narrates: "Al-Muqawqis, the king of the Copts, sent the Prophet (peace and blessings be upon him) a gift and a grey mule, and he ((peace and blessings be upon him)) accepted it."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 3484