Judges 16:8-9

Then the rulers of the Philistines brought her seven fresh bowstrings that had not been dried, and she tied him with them. With men hidden in the room, she called to him, “Samson, the Philistines are upon you!” But he snapped the bowstrings as easily as a piece of string snaps when it comes close to a flame. So the secret of his strength was not discovered.