اَللَّهُمَّ لَكَ رَكَعْتُ وَبِكَ آمَنْتُ وَلَكَ أَسْلَمْتُ خَشَعَ لَكَ سَمْعِيْ وَبَصَرِيْ وَمُخِّيْ وَعِظَامِيْ وَعَصَبِيْ

Allaahumma laka raka'tu, wa bika 'aamantu, wa laka 'aslamtu khasha'a laka sam'ee, wa basaree, wa mukhkhee, wa 'idhaamee, wa 'asabee

O Allah, to You I bow (in prayer) and in You I believe and to You I have submitted. Before You my hearing is humbled, as is my sight, my mind, my bones, my nerves. Ali (RA) said, Rasulullah (ﷺ) used to say these words in rukoo.

Reference: Sahih (Albani). Abu Dawud: 760