عن أبي هريرة رضي الله عنه أن رسول الله صلى الله عليه وسلم‏:‏ نهى عن الخصر في الصلاة‏.‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏‏.‏

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].