John Gill Commentary 1 Samuel 29:5

"Is not this David, of whom they sang one to another in dances, saying, Saul hath slain his thousands, And David his ten thousands?" — 1 Samuel 29:5 (ASV)

[Is] not this David, of whom they sang one to another in dances Long ago:

saying, Saul slew his thousands, and David his ten thousands; so that he is an old sworn enemy of ours; and the more valiant and victorious he has been, the less is he to be trusted, see (1 Samuel 18:7) (21:11).