I am looking for a short story I read a long time ago.
In it, a man dies and finds himself in a dark and featureless afterlife with a disembodied voice that calls itself god.
That god reveals that there is indeed life after death, but only for a selected few, and it consists of nothing more than this void with no contact to others.
Faced with the prospect of eternity alone in that void, the man states his intent to find a way to end his own existence for good. The god answers that it will do anything in its power to prevent that.
After some more back-and-forth the man resolves to find a way to destroy god. God reveals that this is indeed the only reason for the existence of the universe and that afterlife: Because god wishes to find a way to cease to exist.
The story ends, I believe, with something akin to
"The man started to think about the problem. He knew he would succeed eventually; after all he had infinite time"