Musnad Ahmad 32:836

Hajjaj narrated to us, Shu'bah narrated to me, from Qatadah, from Ikrimah, that he said: When this verse was revealed: "Indeed, We have given you a clear conquest, that Allah may forgive for you what preceded of your sin and what will follow" [Al-Fath: 1-2], the companions of the Messenger of Allah (peace and blessings of Allah be upon him) said: "Congratulations and pleasantness to you, O Messenger of Allah. But what is for us?" Then this verse was revealed: "That He may admit the believing men and the believing women to gardens beneath which rivers flow, to abide therein forever, and remove from them their misdeeds" [Al-Fath: 5]. Shu'bah said: Qatadah used to mention this hadith in his stories, from Anas ibn Malik, who said: This verse was revealed when the Messenger of Allah (peace and blessings of Allah be upon him) returned from Al-Hudaybiyyah: "Indeed, We have given you a clear conquest, that Allah may forgive for you what preceded of your sin and what will follow." Then he says: The companions of the Messenger of Allah (peace and blessings of Allah be upon him) said: "Congratulations to you for this." He (Shu'bah) said: I thought that it was all from Anas, so I went to Kufa and narrated it from Qatadah, from Anas. Then I returned and met Qatadah in Wasit, and behold, he was saying: "The first part of it is from Anas, and the last part of it is from Ikrimah." He said: So I went to them in Kufa and informed them of that.