Musannaf Ibn Abi Shayba 34:163

Muhammad ibn al-Hasan narrated to us, Abu 'Awanah narrated to us, from Mughirah, from 'Amir, from 'Adi ibn Hatim, who said: I came to 'Umar among a group of my people. He began to assign a stipend of two thousand [dirhams] to men from Tayy, but he turned away from me. I said, "O Commander of the Faithful, do you not recognize me?" He laughed until he leaned back on his nape, then he said, "By Allah, I do recognize you. You believed when they disbelieved, you came forward when they turned their backs, and you were faithful when they were treacherous. And the first charity that whitened the face of the Messenger of Allah (may Allah bless him and grant him peace) and the faces of his companions was the charity of Tayy." Then he began to apologize, and he said, "I only assigned [the stipend] to a people whom poverty had afflicted, and they are the nobles of their clans, because of the obligations that befall them."