كتاب الصلاة
4
The Book of Prayers
(42)
Chapter: What Is To Be Said While Bowing And Prostrating
(42)
باب مَا يُقَالُ فِي الرُّكُوعِ وَالسُّجُودِ ‏

Ibn Juraij reported:

I asked 'Ata': What do you recite when you are in a state of bowing (in prayer)? He said:" Hallowed be Thou, and with Thy praise, there is no god but Thou." Son of Abd Mulaika narrated to me on the anthority of 'A'isha (who reported): I missed one night the Messenger of Allah (ﷺ) (from his bed). I thought that he might have gone to one of his other wives. I searched for him and then came back and (found him) in a state of bowing, or prostration, saying: Hallowed be Thou and with Thy praise; there is no god but Thou. I said: With my father mayest thou be ransomed and with my mother. I was thinking of (another) affair, whereas you are (occupied) in another one.
وَحَدَّثَنِي حَسَنُ بْنُ عَلِيٍّ الْحُلْوَانِيُّ، وَمُحَمَّدُ بْنُ رَافِعٍ، قَالاَ حَدَّثَنَا عَبْدُ الرَّزَّاقِ، أَخْبَرَنَا ابْنُ جُرَيْجٍ، قَالَ قُلْتُ لِعَطَاءٍ كَيْفَ تَقُولُ أَنْتَ فِي الرُّكُوعِ قَالَ أَمَّا سُبْحَانَكَ وَبِحَمْدِكَ لاَ إِلَهَ إِلاَّ أَنْتَ فَأَخْبَرَنِي ابْنُ أَبِي مُلَيْكَةَ عَنْ عَائِشَةَ قَالَتِ افْتَقَدْتُ النَّبِيَّ صلى الله عليه وسلم ذَاتَ لَيْلَةٍ فَظَنَنْتُ أَنَّهُ ذَهَبَ إِلَى بَعْضِ نِسَائِهِ فَتَحَسَّسْتُ ثُمَّ رَجَعْتُ فَإِذَا هُوَ رَاكِعٌ أَوْ سَاجِدٌ يَقُولُ ‏ "‏ سُبْحَانَكَ وَبِحَمْدِكَ لاَ إِلَهَ إِلاَّ أَنْتَ ‏"‏ ‏.‏ فَقُلْتُ بِأَبِي أَنْتَ وَأُمِّي إِنِّي لَفِي شَأْنٍ وَإِنَّكَ لَفِي آخَرَ ‏.‏
Reference : Sahih Muslim 485
In-book reference : Book 4, Hadith 251
USC-MSA web (English) reference : Book 4, Hadith 985
  (deprecated numbering scheme)