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Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
nasai-kubra:631 – Muḥammad b. Bashhār > Yaḥyá > ʿAbd al-Ḥamīd b. Jaʿfar > Muḥammad b. ʿAṭāʾ > Abū Ḥumayd al-Sāʿidī

"When the Prophet ﷺ bowed he was balanced, he did not make his head higher or lower than his back, and he put his hands on his knees." (Using translation from Nasāʾī 1039)  

الكبرى للنسائي:٦٣١ – أَخْبَرَنَا مُحَمَّدُ بْنُ بَشَّارٍ قَالَ حَدَّثَنَا يَحْيَى قَالَ حَدَّثَنَا عَبْدُ الْحَمِيدِ بْنِ جَعْفَرٍ قَالَ حَدَّثَنِي مُحَمَّدُ بْنُ عَطَاءٍ عَنْ أَبِي حُمَيْدٍ السَّاعِدِيِّ قَالَ

«كَانَ النَّبِيُّ ﷺ إِذَا رَكَعَ اعْتَدَلَ فَلَمْ يَصُبَّ رَأْسَهُ وَلَمْ يُقْنِعْهُ وَوُضِعَ يَدَيْهِ عَلَى رُكْبَتَيْهِ»  

See similar narrations below:

Collected by Nasāʾī
nasai:1039 – Muḥammad b. Bashhār > Yaḥyá > ʿAbd al-Ḥamīd b. Jaʿfar > Muḥammad b. ʿAmr b. ʿAṭāʾ > Abū Ḥumayd al-Sāʿidī

"When the Prophet ﷺ bowed he was balanced, he did not make his head higher or lower than his back, and he put his hands on his knees."  

النسائي:١٠٣٩ – أَخْبَرَنَا مُحَمَّدُ بْنُ بَشَّارٍ قَالَ حَدَّثَنَا يَحْيَى قَالَ حَدَّثَنَا عَبْدُ الْحَمِيدِ بْنُ جَعْفَرٍ قَالَ حَدَّثَنِي مُحَمَّدُ بْنُ عَمْرِو بْنِ عَطَاءٍ عَنْ أَبِي حُمَيْدٍ السَّاعِدِيِّ قَالَ

كَانَ النَّبِيُّ ﷺ إِذَا رَكَعَ اعْتَدَلَ فَلَمْ يَنْصِبْ رَأْسَهُ وَلَمْ يُقْنِعْهُ وَوَضَعَ يَدَيْهِ عَلَى رُكْبَتَيْهِ