Musnad Ahmad 551:14

Yahya ibn Ghaylan narrated to us, he said: Rashdin narrated to us, Musa ibn Ali narrated to me, from his father, from Amr ibn al-Aas, he said: A man said: "O Messenger of Allah, which deed is best?" He said: "Faith in Allah and belief, and striving in the way of Allah, and an accepted Hajj." The man said: "You have increased [the list], O Messenger of Allah." So the Messenger of Allah, peace and blessings of Allah be upon him, said: "Then gentle speech, and the offering of food, and generosity, and good character." The man said: "I want one word." The Messenger of Allah, peace and blessings of Allah be upon him, said to him: "Go, and do not suspect Allah regarding yourself."