Musnad Ahmad 30:1459

'Affan narrated to us, Aban narrated to us, Yahya narrated to us, from Abu Ja'far, from Abu Hurairah, who said: It was said: "O Messenger of Allah, which deeds are best?" He said: "Faith in which there is no doubt, and a military expedition in which there is no misappropriation of spoils, and an accepted Hajj." And Abu Hurairah used to say: "And an accepted Hajj wipes away the sins of that year."