(133) باب السُّجُودِ عَلَى سَبْعَةِ أَعْظُمٍ
Narrated Ibn `Abbas:
The Prophet (ﷺ) was ordered (by Allah) to prostrate on seven parts and not to tuck up the clothes or hair (while praying). Those parts are: the forehead (along with the tip of nose), both hands, both knees, and (toes of) both feet.
Reference: Sahih al-Bukhari 809
In-book reference: Book 10, Hadith 204
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 12, Hadith 773