1 Samuel 17:37-39 New Revised Standard Version (NRSV)
37 David said, “The Lord, who saved me from the paw of the lion and from the paw of the bear, will save me from the hand of this Philistine.” So Saul said to David, “Go, and may the Lord be with you!”
38 Saul clothed David with his armor; he put a bronze helmet on his head and clothed him with a coat of mail. 39 David strapped Saul’s sword over the armor, and he tried in vain to walk, for he was not used to them. Then David said to Saul, “I cannot walk with these; for I am not used to them.” So David removed them.