1 Samuel 21:13-15

13So [fearing for his life] he changed his behavior in their sight, and acted insanely in their hands, and he scribbled on the doors of the gate, and drooled on his beard.

14Then Achish said to his servants, “Look, you see that the man is insane. Why have you brought him to me?

15Do I lack madmen, that you bring this one to behave like a madman in my presence? Shall this one come into my house?”