“The Line of Priesthood from Moses to Adam Is Given; Aaronic Priesthood Conferred upon Aaron and His Seed”

Doctrine and Covenants 84:6–18

6 And the sons of Moses, according to the Holy Priesthood which he received under the hand of his father-in-law, Jethro;
7 And Jethro received it under the hand of Caleb;
8 And Caleb received it under the hand of Elihu;
9 And Elihu under the hand of Jeremy;
10 And Jeremy under the hand of Gad;
11 And Gad under the hand of Esaias;
12 And Esaias received it under the hand of God.
13 Esaias also lived in the days of Abraham, and was blessed of him—
14 Which 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.
18 And the Lord confirmed a priesthood also upon Aaron and his seed, throughout all their generations, which priesthood also continueth and abideth forever with the priesthood which is after the holiest order of God.

President Joseph Fielding Smith wrote:

“The Lord conferred the Holy Priesthood upon Adam and said unto him: ‘Now this same Priesthood, which was in the beginning, shall be in the end of the world also’ (Moses 6:7). The descent of this authority, or divine power, from Adam to Moses is here given in the Lord’s own words to Joseph Smith. Moses received it from Jethro, a priest of the house of Midian. The Midianites were descendants of Abraham, through the children of Keturah, wife of Abraham, therefore the Midianites, who were neighbors to the Israelites in Palestine, were related to the Israelites, and were Hebrews. As descendants of Abraham they were entitled through their faithfulness to his blessings (see Abraham 2:9–11), and in the days of Moses and preceding them, in Midian the priesthood was found.

“We have seen that the Priesthood of Aaron was conferred upon Aaron and his sons by divine command to Moses, when the tribe of Levi was made the official ministers, or priests, of Israel.”

(Church History and Modern Revelation, 2 vols. [1953], 1:337–38.)