Hebrews 7:3, 15, 17, 21

Without father, without mother, without genealogy, having neither beginning of days nor end of life, but made like the Son of God, he remains a priest perpetually.

And this is clearer still, if another priest arises according to the likeness of Melchizedek

For it is attested of Him, “YOU ARE A PRIEST FOREVER ACCORDING TO THE ORDER OF MELCHIZEDEK.”

(for they indeed became priests without an oath, but He with an oath through the One who said to Him, “THE LORD HAS SWORN AND WILL NOT CHANGE HIS MIND, ‘YOU ARE A PRIEST FOREVER’ ”)