Riyad as-Salihin, Book 18, Hadith 1752 (In-Book) ⓘ
Abu Hurairah (May Allah be pleased with him) said: We are prohibited from placing the hand on the side during As-Salat (the prayer).[Al-Bukhari and Muslim].
عن أبي هريرة رضي الله عنه أن رسول الله صلى الله عليه وسلم: نهى عن الخصر في الصلاة. ((متفق عليه)).