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كتاب الأذان
10  
Call to Prayers (Adhaan)
(139)
Chapter: To invoke and glorify Allah in prostration
(139)
باب التَّسْبِيحِ وَالدُّعَاءِ فِي السُّجُودِ
Sahih al-Bukhari 817

Narrated `Aisha:

The Prophet (ﷺ) used to say frequently in his bowing and prostrations "Subhanaka l-lahumma Rabbana wa bihamdika, Allahumma ghfir li" (Exalted [from unbecoming attributes] Are you O Allah our Lord, and by Your praise [do I exalt you]. O Allah! Forgive me). In this way [??] he was acting on what was explained to him in the Holy Qur'an.

حَدَّثَنَا مُسَدَّدٌ، قَالَ حَدَّثَنَا يَحْيَى، عَنْ سُفْيَانَ، قَالَ حَدَّثَنِي مَنْصُورٌ، عَنْ مُسْلِمٍ، عَنْ مَسْرُوقٍ، عَنْ عَائِشَةَ ـ رضى الله عنها ـ أَنَّهَا قَالَتْ كَانَ النَّبِيُّ صلى الله عليه وسلم يُكْثِرُ أَنْ يَقُولَ فِي رُكُوعِهِ وَسُجُودِهِ ‏ "‏ سُبْحَانَكَ اللَّهُمَّ رَبَّنَا وَبِحَمْدِكَ، اللَّهُمَّ اغْفِرْ لِي ‏"‏ يَتَأَوَّلُ الْقُرْآنَ‏.‏
Reference : Sahih al-Bukhari 817
In-book reference : Book 10, Hadith 212
USC-MSA web (English) reference : Vol. 1, Book 12, Hadith 781
  (deprecated numbering scheme)