Sahih Al Bukhari (367)

عن أبي سعيد الخدري أنه قال: نهى رسول الله صلى الله عليه وسلم عن اشتمال الصماء، وأن يحتبي الرجل في ثوب واحد، ليس على فرجه منه شيء.

Abu Sa`id Al Khudry (may Allah be pleased with him) narrated: Allah’s Messenger (peace be upon him) forbade Ishtimal-As-Samma’ (wrapping one’s body with a garment so that one cannot raise its end or take one’s hand out of it). He also forbade Al Ihtiba’ (sitting on buttocks with knees close to abdomen and feet apart with the hands circling the knees) while wrapping oneself with a single garment, without having a part of it over the private parts .