Sahih Muslim Book - 4, Hadith - 1086

حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِى شَيْبَةَ وَأَبُو كُرَيْبٍ قَالاَ حَدَّثَنَا أَبُو مُعَاوِيَةَ عَنِ الأَعْمَشِ عَنْ مُسْلِمٍ عَنْ مَسْرُوقٍ عَنْ عَائِشَةَ قَالَتْ كَانَ رَسُولُ اللَّهِ -صلى الله عليه وسلم- يُكْثِرُ أَنْ يَقُولَ قَبْلَ أَنْ يَمُوتَ « سُبْحَانَكَ وَبِحَمْدِكَ أَسْتَغْفِرُكَ وَأَتُوبُ إِلَيْكَ ». قَالَتْ قُلْتُ يَا رَسُولَ اللَّهِ مَا هَذِهِ الْكَلِمَاتُ الَّتِى أَرَاكَ أَحْدَثْتَهَا تَقُولُهَا قَالَ « جُعِلَتْ لِى عَلاَمَةٌ فِى أُمَّتِى إِذَا رَأَيْتُهَا قُلْتُهَا (إِذَا جَاءَ نَصْرُ اللَّهِ وَالْفَتْحُ) ». إِلَى آخِرِ السُّورَةِ.

It was narrated that 'Aishah said: "The Messenger of Allah (s.a.w) often used to say before he died: 'Subhanak Allahumma! Wa bihamdik. Astaghfiruka wa atubu ilaik (Glory and praise be to You, I ask You for forgiveness and I repent to You.)"' She said: "I said: 'O Messenger of Allah, what are these words that I see that you have started to say?' He said: 'I was given a sign in my Ummah, and when I saw it I was to say these words. "When there comes the Help of Allah and the Conquest (of Makkah)"' until the end of the Surah."