Musannaf Ibn Abi Shayba 33:238

Abu Khalid al-Ahmar narrated to us, from Yahya ibn Sa'id, from Mus'ab ibn Muhammad, from a man from Ghifar, from his father, who said: I arrived with food that I was carrying from al-Jar on camels from the camels of the Sadaqah (charity). Umar examined them, and a young camel among them pleased him. I said, "Take it, O Commander of the Faithful." He struck my shoulder with his hand and said, "By Allah, I am not more entitled to it than a man from the tribe of Ghifar."