The Prophet ﷺ said: "I have been commanded to prostrate on seven bones: on the forehead"- and he pointed with his hand- "on the nose, the hands, the knees and the ends of the feet." (Using translation from Nasāʾī 1097)  

عَنِ النَّبِيِّ ﷺ قَالَ «أُمِرْتُ أَنْ أَسْجُدَ عَلَى سَبْعَةِ أَعْظُمٍ عَلَى الْجَبْهَةِ وَأَشَارَ بِيَدِهِ عَلَى أَنْفِهِ وَالْيَدَيْنِ وَالرُّكْبَتَيْنِ وَأَطْرَافِ الْقَدَمَيْنِ»