Hebrews 7:1-10 (ESV)
The Priestly Order of Melchizedek
7:1 For this Melchizedek, king of Salem, priest of the Most High God, met Abraham returning from the slaughter of the kings and blessed him, 2 and to him Abraham apportioned a tenth part of everything. He is first, by translation of his name, king of righteousness, and then he is also king of Salem, that is, king of peace. 3 He is without father or mother or genealogy, having neither beginning of days nor end of life, but resembling the Son of God he continues a priest forever.
4 See how great this man was to whom Abraham the patriarch gave a tenth of the spoils! 5 And those descendants of Levi who receive the priestly office have a commandment in the law to take tithes from the people, that is, from their brothers,  though these also are descended from Abraham. 6 But this man who does not have his descent from them received tithes from Abraham and blessed him who had the promises. 7 It is beyond dispute that the inferior is blessed by the superior. 8 In the one case tithes are received by mortal men, but in the other case, by one of whom it is testified that he lives. 9 One might even say that Levi himself, who receives tithes, paid tithes through Abraham, 10 for he was still in the loins of his ancestor when Melchizedek met him.