The cuff of the garment is to gather its edges to avoid dust and similar things, and it is disliked to do so during prayer; because it involves arrogance and haughtiness. Ibn Abbas, may Allah be pleased with him, reported that the Prophet, peace be upon him, said: "I was commanded to prostrate on seven parts and not to tuck my hair or garment." This is found in Sahih al-Bukhari 1: 281. See: Al-Mabsut 1: 34.