The Prophet ﷺ used to say in his bowings and prostrations, "Subhanaka Allahumma Rabbanã wa bihamdika, Allãhumma ighfirli" (Glorified be You, O Allah, our Lord! All the praises are for You. O Allah, forgive me)!"
كَانَ النَّبِيُّ ﷺ يَقُولُ فِي رُكُوعِهِ وَسُجُودِهِ سُبْحَانَكَ اللَّهُمَّ رَبَّنَا وَبِحَمْدِكَ اللَّهُمَّ اغْفِرْ لِي