1 Samuel 21:2, 13

David answered Ahimelek the priest, “The king sent me on a mission and said to me, ‘No one is to know anything about the mission I am sending you on.’ As for my men, I have told them to meet me at a certain place.

So 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.