Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: "There are two verses in the Qur'an such that no servant commits a sin, then recites them and seeks forgiveness from Allah, except that he is forgiven." The people asked him about them, but he did not tell them. So Alqamah and al-Aswad said to one another: Come with us. The two of them went home, took the mushaf and began searching in Surah al-Baqarah, and said: We did not find them. Then they searched in Surah al-Nisa until they reached this verse: "And whoever does evil or wrongs himself and then seeks forgiveness of Allah will find Allah Forgiving and Merciful" [Surah al-Nisa: 110], and said: This is one. Then they searched in Surah Al Imran until they reached this verse: "And those who, when they commit an indecency or wrong themselves, remember Allah and seek forgiveness for their sins, and who forgives sins except Allah? And they do not persist in what they have done" [Surah Al Imran: 135]; both of them said: This is the other. Then they closed the mushaf, came to Sayyiduna Abdullah (may Allah be pleased with him) and said: Are these the two verses? He said: "Yes."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9038