This is an event quest that can appear in one of the false Defiled Crypts located in the Cemetery of the Forsaken.
To find the location of this quest, the first thing you should do is to use the Cemetery waypoint in Act 1. Next, you need to find the right tomb. There are three tombs in the graveyard. There is an empty tomb, an ‘event’ tomb and a tomb containing the Chancellor, a boss.
The tomb you are looking for is the event tomb. Inside it you can find the Jar of Souls item, which, upon interaction with it, releases an extended wave of monsters. However, the Jar of Souls will only appear about 40% of the time. During 60% of the time you will instead encounter a ghost that you can speak with to initiate the event quest: The Matriarch’s Bones.
If you do find the Jar of Souls and initiate this event, for one whole minute you must survive an attack by Skeletons and Skeletal Executioners. The low experience reward for this quest is compensated by the fact that the monsters generate experience when slain.
While it is not required in order to complete this event quest, in order to maximize the experience you earn you should engage the spawns instead of kiting them.
Just stay alive until the timer runs out.