The Hands of Moses
A battle in the valley, Moses on the hill above it with his hands lifted, the hands growing heavy, two men holding them up, and the sun going down. Scroll to watch it.
when Moses lifted up his hands, Israel prevailed; but when Moses had let down his hands, Amalek waxed strong. But the hands of Moses were heavy; and they took a stone, and placed it under him, and he sat upon it and Aaron and Hur held up his hands, on the one side and on the other side; and the hands of Moses were made steady even to the setting of the sun.
Exodus 17:11-12, as St Cyprian of Carthage gives it
Moses, for the overthrow of Amalek, who bore the type of the devil, raised up his open hands in the sign and sacrament of the cross, and could not conquer his adversary unless when he had stedfastly persevered in the sign with hands continually lifted up.
Cyprian of Carthage, Treatises