The Prophet (may Allah bless him and give him peace) would place his right hand on the back of his left hand and on his forearm, and at times he would grasp his left hand with his right hand — and he would place both of his hands on his chest.
:عَنْ وَائِلِ بْنِ حُجْرٍ قَالَ
«صَلَّيْتُ مَعَ النَّبِيِّ ﷺ، فَوَضَعَ يَدَهُ الْيُمْنَى عَلَى يَدِهِ الْيُسْرَى عَلَى صَدْرِهِ.»
Translation:
From Wāʾil ibn Ḥujr who said: “I prayed with the Prophet ﷺ, and he placed his right hand upon his left hand on his chest.”
Al-Nasāʾī, Al-Sunan al-Kubrā, Book of Application, Chapter:
Placing the right hand over the left in prayer, Hadith 899.