Musnad Ahmad 664:1

Waki’ narrated to us, from Isma’il ibn Abi Khalid, from his brother, from Abu Kahil, who said—Isma’il said: "I have seen Abu Kahil"—he said: "I saw the Messenger of Allah (peace and blessings of Allah be upon him) addressing the people on the day of Eid while upon a slit-eared she-camel, and an Abyssinian was holding its halter."