Sahih al-Bukhari 478
Sahih al-Bukhari · Book 8: Prayers (Salat) · To clasp one's hands by interlocking the fingers in the mosque or outside the mosque
Narrated Ibn `Umar or Ibn `Amr:
حَدَّثَنَا حَامِدُ بْنُ عُمَرَ ، عَنْ بِشْرٍ ، حَدَّثَنَا عَاصِمٌ ، حَدَّثَنَا وَاقِدٌ ، عَنْ أَبِيهِ ، عَنِ ابْنِ عُمَرَ ، أَوِ ابْنِ عَمْرٍو شَبَّكَ النَّبِيُّ صلى الله عليه وسلم أَصَابِعَهُ.
The Prophet (ﷺ) clasped his hands, by interlacing his fingers.