On how many (parts of the body) does one prostrate on?

Sunan an-Nasa'i · Book 12 · Hadith 1093

أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا حَمَّادٌ، عَنْ عَمْرٍو، عَنْ طَاوُسٍ، عَنِ ابْنِ عَبَّاسٍ، قَالَ أُمِرَ النَّبِيُّ صلى الله عليه وسلم أَنْ يَسْجُدَ عَلَى سَبْعَةِ أَعْضَاءٍ وَلاَ يَكُفَّ شَعْرَهُ وَلاَ ثِيَابَهُ ‏.‏

It was narrated that Ibn 'Abbas said: "The Prophet (ﷺ) was commanded to prostrate on seven parts of his body and not to tuck up his hair or his garment."