It is narrated from Sayyiduna Ibn Mas'ud (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) would often recite «سُبْحَانَكَاللّٰهُمَّوَبِحَمْدِكَاللّٰهُمَّاغْفِرْلِيْ», and when Surah Nasr was revealed to the Prophet (peace and blessings be upon him), he began to say: «سُبْحَانَكَاللّٰهُمَّوَبِحَمْدِكَاللّٰهُمَّاغْفِرْلِيإِنَّكَأَنْتَالتَّوَّابُ» "O Allah! Forgive me, for indeed You are the Acceptor of repentance."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 3891
Hadith Gradingحکم دارالسلام:حسن لغيره، وهذا إسناد ضعيف لانقطاعه، أبو عبيدة لم يسمع من ابن مسعود.