Hebrews 7:21 in the King James Version
(For those priests were made without an oath; but this with an oath by him that said unto him, The Lord sware and will not repent, Thou art a priest for ever after the order of Melchisedec:)
Context
20 Inasmuch as he was not made priest without the taking of an oath
21 (for they indeed have been made priests without an oath), but he with an oath by him that says of him, “The Lord swore and will not change his mind, ‘You are a priest forever, according to the order of Melchizedek.’”
22 By so much, Jesus has become the guarantee of a better covenant.