1 Samuel 21:12-15

12And David laid up these words in his heart, and was sore afraid of Achish the king of Gath.

13And 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.1

14Then said Achish unto his servants, Lo, ye see the man is mad: wherefore then have ye brought him to me?2

15Have I need of mad men, that ye have brought this fellow to play the mad man in my presence? shall this fellow come into my house?