Leviticus 25:40

He shall—serve thee until the year of jubilee— In Exodus 21:2 it is said, that an Hebrew servant being bought should serve only six years, and go out in the seventh. The difference between these passages is supposed to consist in this: that the case in Exodus refers to such slaves as were sold by others; while the present refers to such as sold themselves, and who consequently might dispose of themselves for a longer period than it would have been equitable and humane to have assigned to those who were sold without their own consent.