بُلُوغُ الْمَرَامِ
Bulugh al-Maram 294
The Book of Prayer
وَعَنْ عَائِشَةَ -رَضِيَ اَللَّهُ عَنْهَا- قَالَتْ : { كَانَ رَسُولُ اَللَّهِ - صلى الله عليه وسلم -يَقُولُ: فِي رُكُوعِهِ وَسُجُودِهِ : "سُبْحَانَكَ اَللَّهُمَّ]رَبَّنَا] [1] وَبِحَمْدِكَ , اَللَّهُمَّ اِغْفِرْ لِي } مُتَّفَقٌ عَلَيْهِ [2]
Narrated 'Aishah (RA): Allah's Messenger (ﷺ) used to say while bowing and prostrating Subhanaka Allahumma Rabbana wa bihamdika, Allahumma ighfir li (How Perfect You are, O Allah, Our Rabb, and praise is to You, O Allah, forgive me)." [Agreed upon].
Sunnah.com reference: Book 2, Hadith 180