Sayyiduna Talq bin Ali al-Hanafi (may Allah be pleased with him) narrates that the Prophet (peace and blessings be upon him) said: "Allah Almighty does not look at the prayer of a servant who does not straighten his back between the ruku' (bowing) and the sajdah (prostration)."
Imam Ahmad recorded this narration, and Imam al-Tabarani in al-Mu'jam al-Kabir, and its narrators are thiqat (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2724
Hadith Gradingمحدثین:إسنادہ صحیح۔
Hadith Takhrij«أخرجه مسند أحمد برقم: 15848، وأخرجه المعجم الكبير للطبراني برقم: 8261، وأخرجه الأحاديث المختارة برقم: 182»