وَعَنْ أَبِي هُرَيْرَةَ قَالَ: نَهَى رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ عَن الخصر فِي الصَّلَاة "

Abu Huraira said that God’s Messenger forbade putting the hands on the waist during prayer.

(Bukhari and Muslim.)