Musnad Ahmad 32:62

'Abd al-Wahhab narrated to us, Ayyub narrated to us, from Abu Qilabah, from Anas, that the Prophet, 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 he loves a person, not loving him except for the sake of Allah; and that he hates to return to disbelief after Allah has saved him from it, just as he hates to be cast into a fire."