1 Samuel 27:11-12

And David saved neither man nor woman alive, to bring tidings to Gath, saying, Lest they should tell on us, saying, So did David, and so will be his manner all the while he dwelleth in the country of the Philistines. And Achish believed David, saying, He hath made his people Israel utterly to abhor him; therefore he shall be my servant for ever.