It is narrated from Ali (may Allah be pleased with him) that he said: "When you bow (in ruku‘), recite: 'O Allah! I have bowed for You, and I have humbled myself for You, and I have submitted to Your obedience, and I have believed in You, and I have placed my trust in You, so my bowing is complete for You.'"
Hadith Referenceمسند الإمام الشافعي / كتاب الصلاة / 228
Hadith Takhrijاسنادہ حسن فان عاصم بن ضمرة السلولی الکوفی صدوق حسن الحدیث اخرجہ عبد الرزاق: 2902 - وابن ابی شیبة: (2563)