This quest is a follow-up to the "Ambrus's Prisoners: Fate's Mercy" side quest. You will receive it from one of the freed prisoners.
I freed Danylo, a smith's apprentice, from one of Ambrus's transports. He said I should visit him in Svartrau sometime for a reward.
If I find myself near the market in Svartrau, I should look for the smith's workshop.
Reward: Artisanal Cardinal Bracers (Master Medium Bracers)
I visited Danylo - and just as he'd promised, he rewarded me for saving his life. Looks like good deeds really do pay off.