1 Samuel 21:10-14

Then David set out and fled that day from Saul, and went to Achish king of Gath.

But the servants of Achish said to him, “Is this not David, the king of the land? Did they not sing of this one as they danced, saying, ‘Saul has slain his thousands, And David his ten thousands’?”

David took these words to heart and greatly feared Achish king of Gath.

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?