Abraham received the priesthood from Melchizedek.
14 . . . Abraham received the priesthood from Melchizedek, who received it through the lineage of his fathers, even till Noah;
15 And from Noah till Enoch, through the lineage of their fathers;
16 And from Enoch to Abel, who was slain by the conspiracy of his brother, who received the priesthood by the commandments of God, by the hand of his father Adam, who was the first man—
17 Which priesthood continueth in the church of God in all generations, and is without beginning of days or end of years.
The Prophet Joseph Smith said:
“What was the power of Melchizedek? ‘Twas not the Priesthood of Aaron which administers in outward ordinances, and the offering of sacrifices. Those holding the fulness of the Melchizedek Priesthood are kings and priests of the Most High God, holding the keys of power and blessings. In fact, that Priesthood is a perfect law of theocracy, and stands as God to give laws to the people, administering endless lives to the sons and daughters of Adam.
“Abraham says to Melchizedek, I believe all that thou hast taught me concerning the priesthood and the coming of the Son of Man; so Melchizedek ordained Abraham and sent him away. Abraham rejoiced, saying, Now I have a priesthood.”
(History of the Church, 5:555.)