1 Samuel 21:13-15

13So he pretended to be insane in their presence; and while he was in their hands he acted like a madman, making marks on the doors of the gate and letting saliva run down his beard. 14Achish said to his servants, “Look at the man! He is insane! Why bring him to me? 15Am I so short of madmen that you have to bring this fellow here to carry on like this in front of me? Must this man come into my house?”