1 Samuel 29:5
Is not this David, of whom they sang one to another in dances, saying, Saul slew his thousands, and David his ten thousands? Is not this David, of whom they sang one to another in dances, saying, Saul slew his thousands, and David his ten thousands?
David stood with the Philistine army before its battle with Israel, expected to fight for the Philistines. He could not agree to fight against his own people, since to do so would make him a traitor to Israel and to God. That course could also have cost him the throne.
The verse records the Philistine leaders recalling David's fame among Israel in the song and dance that credited Saul with slain thousands and David with slain ten thousands. They remembered his victory over their champion and Israel's triumph as still fresh in memory. For that reason they feared he might turn against them in the battle to do them great harm, greater harm than Saul's army could do.