Find Kalastor in Lighthaven (2880,1125,0) and say to him Balork
Go to level -4 of the Lighthaven Temple, find Balork, and say the keyword evil.
Afterwards, he will likely try to kill you, but DO NOT KILL HIM.
Return to Kalastor (2880,1125,0) and say nightingale, missions, yes, shake, name, secret, then darkness.
Find Edgar Gimplestratten, a merchant located in a small house to the South-West (2850,1170,0).
Say to him protection and he will attack you. Kill him to get the gold.
Return to Kalastor, he will ask if you have the gold, say yes, yes, then raven's dust.
Reward:
You can repeat this quest as many times as you want.