Exodus 17:8-13

When the Israelites were at Rephidim, they were attacked by the Amalekites. So Moses told Joshua, “Have some men ready to attack the Amalekites tomorrow. I will stand on a hilltop, holding this walking stick that has the power of God.” Joshua led the attack as Moses had commanded, while Moses, Aaron, and Hur stood on the hilltop. The Israelites out-fought the Amalekites as long as Moses held up his arms, but they started losing whenever he had to lower them. Finally, Moses was so tired that Aaron and Hur got a rock for him to sit on. Then they stood beside him and supported his arms in the same position until sunset. That's how Joshua defeated the Amalekites.