1 Samuel 21:2, 13

And David said to Ahimelech the priest, “The king has charged me with a matter and said to me, ‘Let no one know anything of the matter about which I send you, and with which I have charged you.’ I have made an appointment with the young men for such and such a place.

So he changed his behavior before them and pretended to be insane in their hands and made marks on the doors of the gate and let his spittle run down his beard.