Musnad Abu Ya'la al-Mawsili 45:5

Ibrahim ibn Sa'id al-Jawhari narrated to us, Abdullah ibn Bakr narrated to us, from Humayd, from Thabit, from Ishaq ibn Abdullah ibn Abi Talha, from Abu Talha: That the Prophet (peace and blessings of Allah be upon him) sacrificed two white-and-black rams. At the slaughtering of the first, he said: "On behalf of Muhammad and the family of Muhammad." And at the slaughtering of the other, he said: "On behalf of whoever believed in me and affirmed me from my Ummah."