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.