1 Samuel 21:10-15

Then David arose and fled from Saul that day, and went to Achish king of Gath. The servants of Achish said to him, “Is this not David the king of the land? Did they not sing in praise of this one as they danced, saying, ‘Saul has slain his thousands, And David his ten thousands’?” David took these words to heart and was greatly afraid of Achish king of Gath. So [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. Then Achish said to his servants, “Look, you see that the man is insane. Why have you brought him to me? Do I lack madmen, that you bring this one to behave like a madman in my presence? Shall this one come into my house?”