Musnad Abu Ya'la al-Mawsili 115:204

Narrated to us Muhammad ibn Mahdi, narrated to us Abd al-Razzaq, informed us Ma'mar, from Qatadah, from Anas, who said: "Indeed, [the verse] 'That Allah may forgive for you what preceded of your sin and what will follow' (Al-Fath: 2) was revealed to the Prophet, may Allah bless him and grant him peace, upon his return from Al-Hudaybiyyah. The Prophet, may Allah bless him and grant him peace, said: 'A verse has been revealed to me that is more beloved to me than all that is upon the earth.' Then the Messenger of Allah, may Allah bless him and grant him peace, recited it. They said: 'Congratulations and pleasantness to you, O Prophet of Allah! Allah has made clear to you what He will do with you, so what will He do with us?' Then [the verse] was revealed: 'That He may admit the believing men and the believing women...' until He reached '...a great attainment' (Al-Fath: 5)."