Numbers 5:7

then they shall confess their sin which they have done; and he shall recompense his trespass with the principal thereof, and add unto it the fifth part thereof, and give it unto him against whom he hath trespassed. The reference is to some form of trespass which concerned the neighbor's property, the guilt in that case consisting not only in depriving the neighbor of that which was his, but also in disturbing the relation of neighborliness in the people of God and thus in sinning directly against the Lord, Leviticus 6:1.