Reference : Hisn al-Muslim 36

اللّهُـمَّ لَكَ رَكَـعْتُ
 وَبِكَ آمَـنْت، ولَكَ أَسْلَـمْت ،
 خَشَـعَ لَكَ سَمْـعي، وَبَصَـري ،
 وَمُخِّـي، وَعَظْمـي، وَعَصَـبي ،
 وَما استَقَـلَّ بِهِ قَدَمي
Allāhumma laka raka`tu, 
wa bika 'āmantu, wa laka 'aslamtu 
khasha`a laka sam`ee wa baṣarī, 
wa mukhkhī, wa `aẓmī, wa `aṣabī, 
wa mastaqalla bihi qadamī.

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, and my sight, 
and my mind, my bones, my nerves 
and what my feet have mounted upon (for travel).

Reference:
Muslim 1/534, Abu Dawud, An-Nasa'i and At- Tirmidhi.

Chapter: While bowing in prayer