سنن النسائي

It was narrated from Muhammad bin Maslamah that: When the Messenger of Allah (ﷺ) stood to offer a voluntary prayer, he would say when he bowed: "Allahumma laka rak'atu wa bika amantu wa laka aslamtu wa alayka tawwakaltu, anta Rabbi, khasha'a sam'i wa basri wa lahmi wa dammi wa mukhi wa 'asabi Lillahi Rabbil-'Alamin ( O Allah, to You I have bowed, in You I believe, to You I have submitted and in You I put my trust. You are my Lord. My hearing, my sight, my flesh, my blood, my brain and my sinews are humbled before Allah, the Lord of the Worlds)."