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 hair or my clothes; and those seven are: the forehead, the nose, the two hands, the two knees and the two feet."
In Muslim's wording, the words 'la akfita' (I should not gather up) occur in place of 'la akuffa' (I should not tuck up).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2647