The Book of the Commencement of the Prayer
11/10. Chapter:
If the Imam sees a man placing his left hand on his right
Sunan an-Nasai
أَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا عَبْدُ الرَّحْمَنِ، قَالَ حَدَّثَنَا هُشَيْمٌ، عَنِ الْحَجَّاجِ بْنِ أَبِي زَيْنَبَ، قَالَ سَمِعْتُ أَبَا عُثْمَانَ، يُحَدِّثُ عَنِ ابْنِ مَسْعُودٍ، قَالَ رَآنِي النَّبِيُّ صلى الله عليه وسلم وَقَدْ وَضَعْتُ شِمَالِي عَلَى يَمِينِي فِي الصَّلاَةِ فَأَخَذَ بِيَمِينِي فَوَضَعَهَا عَلَى شِمَالِي .
It was narrated that Al Hajjaj bin Abi Zainab said: X"I heard Abu Uthman narrate that Ibn Mas'ud said: 'The Prophet (ﷺ) saw me when I had placed my left hand on my right in prayer. He took hold of my right hand and placed it on my left.'"
Reference : Sunan an-Nasa'i 888In-book reference : Book 11, Hadith 13English translation : Vol. 2, Book 11, Hadith 889