1 Samuel 21:13-17

So he disguised his sanity while in their sight and acted insanely in their custody, and he scribbled on the doors of the gate, and drooled on his beard.

Then Achish said to his servants, “Look, you see the man is behaving like an insane person. Why do you bring him to me?

Do I lack insane people, that you have brought this one to behave like an insane person in my presence? Shall this one come into my house?”