1 Samuel 17:39-40

39David strapped on his sword over his fighting attire and tried to walk around, but he was not used to them. David said to Saul, “I can’t walk in these things, for I’m not used to them.” So David removed them.

40He took his staff in his hand, picked out five smooth stones from the stream, placed them in the pouch of his shepherd’s bag, took his sling in hand, and approached the Philistine.