In both the old and new testaments of the bible the faithful prayed with hands lifted upward. The catacombs dating back to between the 2nd and 4th centuries have frescos of Christians praying with their hands lifted up. The Apostle Paul taught that believers should pray with hands lifted up.
“I desire therefore that the men in every place pray, lifting up holy hands without anger and doubting.” – 1 Timothy 2:8.
“And Solomon stood before the altar of the Lord in the presence of all the congregation of Israel, and spread forth his hands toward heaven” –1 Kings 8:22
I don’t believe there is a “proper” prayer formula, more about the heart. But there no doubt the first Christians prayed with lifted hands not folded hands. This changed sometime after the 4th century. I suspect sometime in the middle ages.
So the question is when and why did the inward gesture of prayer come into practice? I would like to research this and find a specific answer.