1 Samuel 21:14

“Then said Achish to his servants, lo, you see the man is mad, etc.] Which he said, as willing his servants should think so, and therefore rather the object of their pity than of their rage and malice; or as really believing he was so, which he and they might conclude not merely from these his actions, before described, which they might judge real and not feigned; but they might suppose this was truly his case, brought upon him by the ill usage of Saul, who pursuing him from place to place, and sending after him to take away his life, had really brought him to distraction; and this they might rather conclude from his coming to Gath, an enemy’s country, and whose champion he had slain, and…”

“is mad: or, playeth the madman, Ecc 7:7 Next: 1 Kings (1 Samuel) Chapter 22”

“By this dissimulation David escaped the danger which threatened him; for Achish thought him mad, and would have nothing to do with him. "Wherefore do ye bring him to me? Have I need of madmen, that ye have brought this man hither to rave against me? Shall this man come into my house?" Thus Achish refused to receive him into his house. But whether he had David taken over the border, or at any rate out of the town; or whether David went away of his own accord; or whether he was taken away by his servants, and then hurried as quickly as possible out of the land of the Philistines, is not expressly mentioned, as being of no importance in relation to the principal object of the narrative. All…”