Another Mission for the Temple - Baldur's Gate 2 Side Quest
Another Mission for the Temple is the final side quest given to you by the temples in the Temple District of Athkatla. This quest can be started immediately after you finish the Gain the Services of Sir Sarles for the Temple side quest. Speak with the same NPC you turned the previous quest in at and they'll offer you this one.
Depending on what temple starts this quest for you the first step will be slightly different. For most people you'll probably have to visit Dawnmaster Sain in the Temple of Lathander first then he'll tell you to go speak with Travin in the Slums District at night. At this point all quests will converge and it will be the same for everyone here on out.
You can find Travin in the northern portion of the Slums District at hour 22+ (check the clock in the bottom right of the screen to see the time). A screenshot of the exact location you can find Travin is shown below.
Travin will tell you that the person currently holding the ring is a man named Borinall whose also found in the Slums District. Borinall's House is marked on the map; it's located on the large platform in the center of the map above the Copper Coronet. Inside you'll meet a man named Borinall who will ask you to prove yourself by declaring your loyalty to Talos.
If you were sent by the Temple of Talos then this test is no big deal, however, if either of the other 2 temples sent you then you will fail this test. Failing this test means you'll have to kill Borinall for the ring, if you pass it then he'll give the ring to you. This is really the only difference between the 2. You can also refuse to take the test in which case it'll play out as if you failed it.
Regardless of what outcome you choose here once you get the Dawn Ring it's time to return to the temple who hired you. Dawnbringer Sain is who you'll return it to if you're working for Helm or Lathander and Talon Yarryl is who you'll turn it into if you're working for Talos.