Majma al-Zawaid — Hadith 14243

Sayyidah Umm Salamah (may Allah be pleased with her) narrates: Before his passing, the Prophet (peace and blessings be upon him) used to say often: "Subhanakallahumma wa bihamdika, astaghfiruka wa atubu ilayk (Glory be to You, O Allah, and praise be to You; I seek Your forgiveness and I repent to You)." I said: "O Messenger of Allah, I have seen that you often say: 'Subhanakallahumma wa bihamdika, astaghfiruka wa atubu ilayk (Glory be to You, O Allah, and praise be to You; I seek Your forgiveness and I repent to You).'" The Prophet (peace and blessings be upon him) said: "I have been commanded to do so." Then he recited this surah (Allah Almighty says): "When the help of Allah and the victory come."
Al-Tabarani recorded it in al-Mu'jam al-Saghir, and its narrators are the narrators of the "Sahih".