It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) said: "I have been commanded to prostrate on seven bones: on the forehead" and he (peace and blessings be upon him) pointed with his hand to his nose "and on the two hands, the knees and the edges of the feet, and that we should not tuck up our clothes or our hair." In the hadith of Mu'alla it is: "and that I should not tuck up my hair or my clothes."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2646