It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "I have been commanded to prostrate on seven limbs, and not to tuck up my garment or my hair (in prostration)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10960