Sahih Muslim Book 4, Hadith Number 994.

Chapter : The excellence of prostration and exhortation to observe it.

Ibn Abbas reported that the Messenger of Allah (may peace be upon him) said: I have been commanded to prostrate myself on seven bones: “forehead,” and then pointed with his hand towards his nose, hands, feet, and the extremities of the feet; and we were forbidden to fold back clothing and hair.