1 - Sahih Muslim [#:991] Ibn 'Abbas reported: The Apostle of Allah (may peace be upon him) had been commanded that he should prostrate on the seven (bones) and he was forbidden to fold back the hair and clothing. And in the narration transmitted by Abu Rabi' (the words are):" on the seven bones and I was forbidden to fold back the hair and clothing". According to Abu'l-Rabi' (the seven bones are): The hands, the knees, and the (extremities) of the feet and the forehead.
2 - Sahih Bukhari [#:777]Narrated Ibn `Abbas: The Prophet said, "We have been ordered to prostrates on seven bones and not to tuck up the clothes or hair."
3 - Sahih Bukhari [#:779]Narrated Ibn `Abbas: The Prophet said, "I have been ordered to prostrate on seven bones i.e. on the forehead along with the tip of the nose and the Prophet pointed towards his nose, both hands, both knees and the toes of both feet and not to gather the clothes or the hair."