(133) CHAPTER. To prostrate on seven bones.
Narrated Ibn `Abbas: The Prophet 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.
Narrated Ibn `Abbas: The Prophet said, We have been ordered to prostrates on seven bones and not to tuck up the clothes or hair.
Narrated Al-Bara' bin `Azib: (He was not a liar) We used to pray behind the Prophet and when he said, Sami`a l-lahu liman hamidah , none of us would bend his back (to go for prostration) till the Prophet had placed his, forehead on the ground.