Musnad Ahmad 32:840

Al-Mu'ammal ibn Isma'il and 'Affan narrated to us, they said: Hammad ibn Salamah narrated to us, Thabit narrated to us, from Anas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "There are three things, whoever possesses them will find the sweetness of faith through them: that Allah and His Messenger are more beloved to him than anything else besides them; that the servant dislikes to return to disbelief just as he dislikes to be cast into the Fire; and that the servant loves a servant, not loving him except for the sake of Allah."