Hebrews 7:4-6

4Just think how great he was: Even the patriarch Abraham gave him a tenth of the plunder! 5Now the law requires the descendants of Levi who become priests to collect a tenth from the people—that is, from their fellow Israelites—even though they also are descended from Abraham. 6This man, however, did not trace his descent from Levi, yet he collected a tenth from Abraham and blessed him who had the promises.