1 Samuel 21:2, 13

David said to Ahimelech the priest, “The king has commissioned me with a matter and has said to me, ‘Let no one know anything about the matter on which I am sending you and with which I have commissioned you; and I have directed the young men to a certain place.’

So he disguised his sanity before them, and acted insanely in their hands, and scribbled on the doors of the gate, and let his saliva run down into his beard.