The Messenger of Allah ﷺ, when he stood to perform a voluntary prayer, would say upon bowing, "O Allah, to You I have bowed, in You I have believed, to You I have submitted, and upon You I rely. You are my Lord. My hearing, my sight, my flesh, my blood, my brain, and my nerves are humbled before Allah, Lord of all the worlds."
أخبرنا يحيى بن عثمان قال حدثنا ابن حمير قال حدثنا شعيب عن محمد بن المنكدر وذكر آخر قبله عن عبد الرحمن الأعرج
أن رسول الله ﷺ كان إذا قام يصلي تطوعا يقول إذا ركع اللهم لك ركعت وبك آمنت ولك أسلمت وعليك توكلت أنت ربي خشع سمعي وبصري ولحمي ودمي ومخي وعصبي لله رب العالمين
Sahih. Related by Tabarani in Al-Kabir 19/231, 232, no. 515, from the hadith of Muhammad bin Humayr, at length. It is also found in Al-Kubra, no. 639, and part of it was mentioned earlier, no. 897. Its chain of transmission is hasan, and it has many corroborating narrations, among them the preceding hadith.