The Messenger of Allah ﷺ used to place his right hand on his left hand, then he folded them strictly on his chest in prayer.
كَانَ رَسُولُ اللَّهِ ﷺ يَضَعُ يَدَهُ الْيُمْنَى عَلَى يَدِهِ الْيُسْرَى ثُمَّ يَشُدُّ بَيْنَهُمَا عَلَى صَدْرِهِ وَهُوَ فِي الصَّلاَةِ