Musnad Abu Ya'la al-Mawsili 117:5

Narrated to us 'Abd al-A'la, narrated to us Hammad, from Thabit, from Anas, that the Messenger of Allah (may Allah bless him and grant him peace) said: "Three things, whoever possesses them will find the sweetness of faith: that Allah and His Messenger are more beloved to him than that he should return to being a Jew or a Christian."