مِشْكَاةُ الْمَصَابِيحِ
Mishkat al-Masabih 981
Prayer
What may not be done during Prayer and what is permitted - Section 1
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.)
Mishkat al-Masabih, 981مُتَّفَقٌ عَلَيْهِ (الألباني)