1 Samuel 21:12 (KJV)

Now a certain man of the servants of Saul was there that day, detained before the LORD; and his name was Doeg, an Edomite, the chiefest of the herdmen that belonged to Saul.

And David said unto Ahimelech, And is there not here under thine hand spear or sword? for I have neither brought my sword nor my weapons with me, because the king's business required haste.

And the priest said, The sword of Goliath the Philistine, whom thou slewest in the valley of Elah, behold, it is here wrapped in a cloth behind the ephod: if thou wilt take that, take it: for there is no other save that here. And David said, There is none like that; give it me.

And David arose and fled that day for fear of Saul, and went to Achish the king of Gath.

And the servants of Achish said unto him, Is not this David the king of the land? did they not sing one to another of him in dances, saying, Saul hath slain his thousands, and David his ten thousands?

And he changed his behaviour before them, and feigned himself mad in their hands, and scrabbled on the doors of the gate, and let his spittle fall down upon his beard.

Then said Achish unto his servants, Lo, ye see the man is mad: wherefore then have ye brought him to me?

Have I need of mad men, that ye have brought this fellow to play the mad man in my presence? shall this fellow come into my house?