Musnad Ahmad 32:1463

Yunus and Hassan ibn Musa narrated to us, they said: Hammad ibn Salamah narrated to us, from Thabit al-Bunani, from Anas ibn Malik, 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: that Allah and His Messenger are more beloved to him than anything else besides them; and that a man loves a person, not loving him except for the sake of Allah; and that a man would hate to be cast into the Fire more than he would hate to return to Judaism or Christianity." Hassan said: "Or Christianity."