Now David took these words to heart, and was very much afraid of Achish the king of Gath.
1 Samuel 21:12
Surrounding context
21:11 And the servants of Achish said to him, "Is this not David the king of the land? Did they not sing of him to one another in dances, saying: "Saul has slain his thousands, And David his ten thousands'?"
21:12 Now David took these words to heart, and was very much afraid of Achish the king of Gath.
21:13 So he changed his behavior before them, pretended madness in their hands, scratched on the doors of the gate, and let his saliva fall down on his beard.