I found a source for that supposed reasoning of Russell:
Faith on the March by A.H. Macmillan (Prentice-Hall 1957) page 18 says:
At the age of seventeen, then, this had become his conclusion: "Now my father is in business here in Pittsburgh and is doing quite well. There is no use in my trying to find out anything reasonable about the future from any of the creeds or even from the Bible, so I’m just going to forget the whole thing and give all my attention to business. If I make some money I can use that to help suffering humanity, even though I cannot do them any good spiritually."
However, Macmillan does not provide a source for this quote. Since 1957 is a long time after 1869, I would like to see if the source could be traced back further.