Sayyiduna Abu Hurayrah (may Allah be pleased with him) said that the Prophet (peace and blessings be upon him) forbade two ways of dressing: "The first is that a man sits with his knees drawn up (ihtiba') in such a way that nothing comes between his private parts and the sky; and the second is that a person wears his garment with one of his sides exposed, throwing his garment over his shoulder."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجمعة / 5919