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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
bukhari:3564 – Qutaybah b. Saʿīd > Bakr b. Muḍar > Jaʿfar b. Rabīʿah > al-Aʿraj > ʿAbdullāh b. Mālik Ibn Buḥaynah al-Asdī

When the Prophet ﷺ prostrated, he used to keep his arms so widely apart that we used to see his armpits. (The sub-narrator, Ibn Bukair said, "The whiteness of his armpits.")  

البخاري:٣٥٦٤ – حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ حَدَّثَنَا بَكْرُ بْنُ مُضَرَ عَنْ جَعْفَرِ بْنِ رَبِيعَةَ عَنِ الأَعْرَجِ عَنْ عَبْدِ اللَّهِ بْنِ مَالِكٍ ابْنِ بُحَيْنَةَ الأَسْدِيِّ قَالَ

كَانَ النَّبِيُّ ﷺ إِذَا سَجَدَ فَرَّجَ بَيْنَ يَدَيْهِ حَتَّى نَرَى إِبْطَيْهِ قَالَ وَقَالَ ابْنُ بُكَيْرٍ حَدَّثَنَا بَكْرٌ بَيَاضَ إِبْطَيْهِ  

See similar narrations below:

Collected by Ibn Ḥibbān

ذِكْرُ مَا يُسْتَحَبُّ لِلْمُصَلِّي أَنْ يُجَافِيَ فِي سُجُودِهِ حَتَّى يُرَى بَيَاضُ إِبْطَيْهِ

ibnhibban:1919 – ʿUmar b. Muḥammad al-Hamdānī > Muḥammad b. Sahl b. ʿAskar > Abū al-Aswad al-Naḍr b. ʿAbd al-Jabbār > Bakr b. Muḍar > Jaʿfar b. Rabīʿah > ʿAbd al-Raḥman b. Hurmuz al-Aʿraj > Ibn Buḥaynah

[Machine] "The Prophet ﷺ used to raise his hands and spread them in front of him during prostration until the whiteness of his armpits was visible."  

ابن حبّان:١٩١٩ – أَخْبَرَنَا عُمَرُ بْنُ مُحَمَّدٍ الْهَمْدَانِيُّ قَالَ حَدَّثَنَا مُحَمَّدُ بْنُ سَهْلِ بْنِ عَسْكَرٍ قَالَ حَدَّثَنَا أَبُو الْأَسْوَدِ النَّضْرُ بْنُ عَبْدِ الْجَبَّارِ قَالَ حَدَّثَنَا بَكْرُ بْنُ مُضَرٍ عَنْ جَعْفَرِ بْنِ رَبِيعَةَ عَنْ عَبْدِ الرَّحْمَنِ بْنِ هُرْمُزَ الْأَعْرَجِ عَنِ ابْنِ بُحَيْنَةَ قَالَ

«كَانَ النَّبِيُّ ﷺ إِذَا سَجَدَ فَرَّجَ بَيْنَ يَدَيْهِ حَتَّى يَبْدُوَ بَيَاضُ إِبْطَيْهِ»