كتاب الصلاة
4  
The Book of Prayers
(46)
Chapter: The Description Of The Prayer, With What It Begins And Ends. The Description Of Bowing And Moderation Therein, And Of Prostration And Moderation Therein. Tashah-hud After Each Two Rak'ah Of Four Rak'ah Prayers. Description Ol Sitting Between The Two Prostrations, And In The First Tashah-hud
(46)
باب مَا يَجْمَعُ صِفَةَ الصَّلاَةِ وَمَا يُفْتَتَحُ بِهِ وَيُخْتَمُ بِهِ وَصِفَةَ الرُّكُوعِ وَالاِعْتِدَالِ مِنْهُ وَالسُّجُودِ وَالاِعْتِدَالِ مِنْهُ وَالتَّشَهُّدِ بَعْدَ كُلِّ رَكْعَتَيْنِ مِنَ الرُّبَاعِيَّةِ وَصِفَةَ الْجُلُوسِ بَيْنَ السَّجْدَتَيْنِ وَفِي التَّشَهُّدِ الأَوَّلِ
Sahih Muslim 495 b

This hadith has been narrated by Ja'far b. Rabi' with the same chain of transmitters. And in the narration transmitted by 'Amr b. al-Harith (the words are):

" When the Messenger of Allah (rtiay peace be upon him) prostrated, he spread out his arms so that the whiteness of his armpits was visible." And in the narration transmitted by al-Laith (the words are:" When the Messenger of Allah (ﷺ) prostrated. he spread his hands from the armpits so that I saw their whiteness."
حَدَّثَنَا عَمْرُو بْنُ سَوَّادٍ، أَخْبَرَنَا عَبْدُ اللَّهِ بْنُ وَهْبٍ، أَخْبَرَنَا عَمْرُو بْنُ الْحَارِثِ، وَاللَّيْثُ بْنُ سَعْدٍ، كِلاَهُمَا عَنْ جَعْفَرِ بْنِ رَبِيعَةَ، بِهَذَا الإِسْنَادِ ‏.‏ وَفِي رِوَايَةِ عَمْرِو بْنِ الْحَارِثِ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِذَا سَجَدَ يُجَنِّحُ فِي سُجُودِهِ حَتَّى يُرَى وَضَحُ إِبْطَيْهِ ‏.‏ وَفِي رِوَايَةِ اللَّيْثِ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ إِذَا سَجَدَ فَرَّجَ يَدَيْهِ عَنْ إِبْطَيْهِ حَتَّى إِنِّي لأَرَى بَيَاضَ إِبْطَيْهِ ‏.‏
Reference : Sahih Muslim 495b
In-book reference : Book 4, Hadith 268
USC-MSA web (English) reference : Book 4, Hadith 1001
  (deprecated numbering scheme)