Mishkat al-Masabih 887
Ibn ‘Abbas reported God’s Messenger as saying, “I have been commanded to prostrate myself on seven bones:
the forehead, the hands, 1 the knees, and the extremities of the feet, 2 and not to fold back the clothing or the hair.”

1. i.e. the palms.
2. i.e. the toes.

(Bukhari and Muslim.)
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»