Musnad Ahmad 27:1181

Yahya ibn Adam narrated to us, Zuhayr narrated to us, from Musa ibn Uqbah, from Salim ibn Abdullah ibn Umar, from Abdullah ibn Umar, that when the Messenger of Allah (peace and blessings of Allah be upon him) appointed Usamah, it reached him that the people were criticizing Usamah and finding fault with his leadership. He stood up—as Salim narrated to me—and said: "You are criticizing Usamah and finding fault with his leadership, just as you did with his father before him. Indeed, he was worthy of leadership, and he was among the most beloved of all people to me. And this son of his, after him, is among the most beloved of people to me, so treat him well, for he is among the best of you."