Silsilat al-Ahadith al-Sahihah

Abdullah bin Buraidah narrates from his father that he (the Prophet) forbade two types of sitting and two types of clothing. The two types of sitting are: (1) sitting between sunlight and shade, and (2) sitting in such a way with one garment that the private parts become exposed. And the two types of clothing are: (1) performing prayer in one garment without properly covering oneself, and (2) performing prayer wearing only trousers without covering the upper part of the body with a sheet.