Tehillim 110:4

Orthodox Jewish Bible

^4 (5) Hashem hath sworn, and will not relent, Thou [Moshiach] art a kohen l’olam al divrati Malki-Tzedek (kohen forever in respect to the order of Malki-Tzedek; [see Bereshis 14:18; note it is the kohen who makes kapporah for sin—see Leviticus 4:20; Isa 53:8).