Musnad Ahmad 32:502

Zayd ibn al-Hubab narrated to us, Suhayl, the brother of Hazm, informed me, Thabit al-Bunani narrated to us, from Anas ibn Malik, who said: The Messenger of Allah, peace and blessings of Allah be upon him, recited this verse: "He is worthy of fear and worthy of forgiveness" [Al-Muddaththir: 56]. He said: "Your Lord says: 'I am worthy that I should be feared, so let no god be set up with Me. Whoever fears that he should set up a god with Me, he is worthy that I should forgive him.'"