Hadith 242

Riyad as-Salihin

Book 17: The Book of the Prohibited actions

Chapter 338

Prohibition of Placing the hands on the sides during As-Salat (The Prayer)

باب كراهة وضع اليد على الخاصرة في الصلاة

Riyad as-Salihin 1752
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].