Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates: We used to think that there would be no room for repentance for a person who fell into trial, that is, when he had abandoned his religion after accepting Islam and after coming to know it. Then Allah Almighty revealed this verse concerning those people: "O My servants who have wronged themselves! Do not despair of the mercy of Allah." After this, the narrator mentioned the full hadith, which has already passed in the chapter on the military expeditions and the Hijrah. Its chain contains Ibn Ishaq, who is thiqah (trustworthy) but a mudallis. (Allamah Haythami says:) I say: The hadith narrated by Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) is in Surah al-Talaq.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب التفسير / 11315