1 Samuel 17:39-40

39David strapped his sword over the tunic and tried to walk, but he was not accustomed to them.

“I cannot walk in these,” David said to Saul. “I am not accustomed to them.” So David took them off. 40And David took his staff in his hand, selected five smooth stones from the brook, and put them in the pouch of his shepherd’s bag. And with his sling in hand, he approached the Philistine.