I Samuel 21:10-15

Then David arose and fled that day from before Saul, and went to Achish the king of Gath. And the servants of Achish said to him, “Is this not David the king of the land? Did they not sing of him to one another in dances, saying: ‘Saul has slain his thousands, And David his ten thousands’?” Now David took these words to heart, and was very much afraid of Achish the king of Gath. So he changed his behavior before them, pretended madness in their hands, scratched on the doors of the gate, and let his saliva fall down on his beard. Then Achish said to his servants, “Look, you see the man is insane. Why have you brought him to me? Have I need of madmen, that you have brought this fellow to play the madman in my presence? Shall this fellow come into my house?”