عَنِ ابْنِ عَبَّاسٍ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «أُمِرْتُ أَنْ أَسْجُدَ عَلَى سَبْعَةِ أَعْظُمٍ عَلَى الْجَبْهَةِ وَالْيَدَيْنِ وَالرُّكْبَتَيْنِ وَأَطْرَافِ الْقَدَمَيْنِ وَلَا نَكْفِتَ الثِّيَاب وَلَا الشّعْر»

‘Abdallah b. Malik Ibn Buhaina* said that when the Prophet prostrated himself he spread out his arms so that the whiteness under his armpits was visible. * Buhaina was ‘Abdallah’s mother.(Bukhari and Muslim.)