Musnad Ahmad 541:3

'Abd al-Rahman narrated to us, Musa ibn 'Ali narrated to us, from his father, who said: I heard 'Amr ibn al-'As saying: The Messenger of Allah (peace and blessings of Allah be upon him) sent for me and said: "Take your clothes and your weapon, then come to me." So I came to him while he was performing ablution. He looked up at me, then lowered his gaze and said: "I intend to send you with an army, so Allah will keep you safe and grant you spoils, and I desire for you a good portion of wealth." I said: "O Messenger of Allah, I did not embrace Islam for the sake of wealth, but I embraced Islam out of a desire for Islam, and to be with the Messenger of Allah (peace and blessings of Allah be upon him)." He said: "O 'Amr, excellent is the good wealth for the righteous man."