Genesis
14:18 And Melchizedek king of Salem brought forth bread and wine: and he [was] the priest of the most high God.
Psalms
110:4 The LORD hath sworn, and will not repent, Thou [art] a priest for ever after the order of Melchizedek.
Hebrews
5:6 As he saith also in another [place], Thou [art] a priest for ever after the order of Melchisedec.
5:10 Called of God an high priest after the order of Melchisedec.
6:20 Whither the forerunner is for us entered, [even] Jesus, made an high priest for ever after the order of Melchisedec.
7:1 For this Melchisedec, king of Salem, priest of the most high God, who met Abraham returning from the slaughter of the kings, and blessed him;
7:10 For he was yet in the loins of his father, when Melchisedec met him.
7:11 If therefore perfection were by the Levitical priesthood, (for under it the people received the law,) what further need [was there] that another priest should rise after the order of Melchisedec, and not be called after the order of Aaron?
7:15 And it is yet far more evident: for that after the similitude of Melchisedec there ariseth another priest,
7:17 For he testifieth, Thou [art] a priest for ever after the order of Melchisedec.
7:21 (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:)

Melchizedek is not a simple reference. Many (sometimes tedious) articles. Here is one perplexing poem.

73. Melchizedek
By John Henry, Cardinal Newman  (1801–1890)
  
Without father, without mother, without descent; having neither beginning of days, nor end of life.

THRICE bless’d are they, who feel their loneliness;
To whom nor voice of friends nor pleasant scene
Brings that on which the sadden’d heart can lean;
Yea, the rich earth, garb’d in her daintiest dress
Of light and joy, doth but the more oppress,        5
Claiming responsive smiles and rapture high;
Till, sick at heart, beyond the veil they fly,
Seeking His Presence, who alone can bless.
Such, in strange days, the weapons of Heaven’s grace;
When, passing o’er the high-born Hebrew line,       10
He forms the vessel of His vast design;
Fatherless, homeless, reft of age and place,
Sever’d from earth, and careless of its wreck,
Born through long woe His rare Melchizedek.