Musnad Abu Ya'la al-Mawsili 113:23

Ishaq narrated to us, Abd al-Wahhab narrated to us, from Ayyub, from Abu Qilabah, 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 through them: that Allah and His Messenger are more beloved to him than anything else besides them; that he loves a person, not loving him except for the sake of Allah; and that he hates to return to disbelief just as he hates to have a fire kindled for him and be cast into it."