'Reward' in the Bible

when one told me, saying, ‘Behold, Saul is dead,’ and thought he was bringing good news, I seized him and killed him in Ziklag, which was the reward I gave him for his news.

Now Ahimaaz the son of Zadok said once more to Joab, “But whatever happens, please let me also run after the Cushite.” And Joab said, “Why would you run, my son, since you will have no reward for going?”

Your servant would merely cross over the Jordan with the king. Why should the king compensate me with this reward?