It was narrated that Ibn Mas’ud said:“The Messenger of Allah (ﷺ) said: ‘When anyone of you bows, let him say in his bowing: “Subhana Rabbiyal-‘Azim (Glory is to my Lord, the Most Great)” three times; if he does that his bowing will be complete. And when anyone of you prostrates, let him say in his prostration, ‘Subhana Rabbiyal-A’la (Glory if to my Lord, the Most High)” three times; if he does that, his prostration will be complete, and that is the minimum.’”
حَدَّثَنَا أَبُو بَكْرِ بْنُ خَلاَّدٍ الْبَاهِلِيُّ، حَدَّثَنَا وَكِيعٌ، عَنِ ابْنِ أَبِي ذِئْبٍ، عَنْ إِسْحَاقَ بْنِ يَزِيدَ الْهُذَلِيِّ، عَنْ عَوْنِ بْنِ عَبْدِ اللَّهِ بْنِ عُتْبَةَ، عَنِ ابْنِ مَسْعُودٍ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " إِذَا رَكَعَ أَحَدُكُمْ فَلْيَقُلْ فِي رُكُوعِهِ سُبْحَانَ رَبِّيَ الْعَظِيمِ . ثَلاَثًا فَإِذَا فَعَلَ ذَلِكَ فَقَدْ تَمَّ رُكُوعُهُ وَإِذَا سَجَدَ أَحَدُكُمْ فَلْيَقُلْ فِي سُجُودِهِ سُبْحَانَ رَبِّيَ الأَعْلَى ثَلاَثًا. فَإِذَا فَعَلَ ذَلِكَ فَقَدْ تَمَّ سُجُودُهُ، وَذَلِكَ أَدْنَاهُ " .
IbnMaja
Establishing the Prayer and the Sunnah Regarding Them • Hadith 890