1 Samuel 17:49-50 NIV

49 Reaching into his bag and taking out a stone, he slung it and struck the Philistine on the forehead. The stone sank into his forehead, and he fell facedown on the ground.
50 So David triumphed over the Philistine with a sling1 and a stone; without a sword in his hand he struck down the Philistine and killed him.

References for 1 Samuel 17:50