Proverbs 28:8

unjust gain Rather, increase, as A.V. marg. and R.V. text, μετὰ τόκων καὶ πλεονασμῶν, LXX. Comp. Leviticus 25:36-37.

The idea of its being "unjust" is implied by the word "usury" with which it is associated. The R.V. gives augmenteth, instead of increaseth, in the former part of the verse, as the Heb. word is not the same, as it there renders increase.