2 Samuel 4:10

When one told me, saying, behold, Saul is dead
No more is related, not that he killed him, or assisted in killing him, only that he was dead; by which it appears, as Abarbinel thinks, that the Amalekite did not slay Saul, and that David did not put him to death on that account, but for what follows:

thinking to have brought good tidings;
which would have been very acceptable to David, that he would have rejoiced and exulted at it as he did; but he was mistaken; instead of that,

I took hold of him, and slew him at Ziklag;
that is, ordered one of his young men to lay hold on him, and slay him, as he did, ( 2 Samuel 1:15 ) ;

who [thought] that I would have given him a reward for his tidings;
a handsome present, as the Targum here, a gift, or raised him to some post of honour and profit.