Dear tivtrans,
One thing I would like to know: this text, which your friend wants translated, is it written by a native-English speaking author? Speaking from my own experience, I could well imagine that an author who is proud of his acquired skill in idiomatic English actually "creates" a new application of a suggestive expression picked up in a different context. So it would seem vain to look for a historical origin. I am pretty sure the author meant "wealth accumulated by hard work".