Musnad Ahmad 30:1489

Hassan narrated to us, Ibn Lahi'ah narrated to us, Abu Yunus narrated to us, from Abu Hurairah, from the Messenger of Allah (peace and blessings of Allah be upon him), who said: "Indeed, Allah the Almighty and Majestic said: 'My servant has denied Me, and it was not for him to deny Me. And My servant has insulted Me, and it was not for him to insult Me. As for his denying Me, he says: "He will not bring me back as He began me," and the beginning of creation is not easier for Me to bring back than its end. So he has denied Me if he says that. And as for his insulting Me, he says: "Allah has taken a son," while I am Allah, the One, the Eternal Refuge; I do not beget, nor was I begotten.'"