It is narrated from Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) that when the Messenger of Allah (peace and blessings be upon him) began an obligatory prayer; then the full hadith was mentioned. In it is that when he (peace and blessings be upon him) bowed he would say: 'Allahumma laka raka'tu, wa bika amantu, wa laka aslamtu, anta rabbi, khasha'a laka sam'i wa basari wa mukhkhi wa 'azmi wa ma istaqallat bihi qadami lillahi rabbi al-'alamin' (O Allah, to You alone I have bowed, in You I have believed, and to You I have submitted; You are my Lord; my hearing, my sight, my brain, my bones, and the body that my feet carry are all humbled before You. You are the Lord of all the worlds).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2564