Wiktionary
sweat of one's brow
n. (context idiomatic English) The effort extended in labor, and the value created thereby.
Usage examples of "sweat of one's brow".
From the moment they cared if they didn't it was living by the sweat of one's brow.
This was a common extension of the Biblical injunction about working for one's daily bread in the sweat of one's brow.