This is another Qeynos Bounty quest. It starts by talking to Gil McMartin in the Commonlands next to the West Freeport gates.
Gil sends you to kill Xarix Sabertooth in Thundering Steppes. He spawns near 240,-7,-740 as a single up arrow mob at the level of the quest holder. Kill Xarix and return to Gil McMartin in the Commonlands to collect your bounty.