1 Samuel 21:13
And he changed his behaviour before them, and feigned himself mad in their hands, and scrabbled on the doors of the gate, and let his spittle fall down upon his beard. And he changed his behaviour before them, and feigned himself mad in their hands, and scrabbled on the doors of the gate, and let his spittle fall down upon his beard.
The incident took place in Gath, where David was away from his own people and detained among the Philistines, Israel's enemies, before Achish and his men. There he changed his behavior and feigned madness, acting as though insane by marking and scraping on the doors of the gate and letting his spittle run down upon his beard. This deception enabled him to escape the danger he faced there among his enemies.
Such extraordinary action stands as an example of the Spirit of God leading someone held away from his own people to act in an extraordinary way for deliverance.