Article of Faith 5

Elder David A Bednar, The Powers of Heaven, April 2012 General Conference
"Thus, a boy or a man receives the authority of the priesthood and is ordained to a specific office by one who already holds the priesthood and has been authorized by a leader with the necessary priesthood keys."

Article of Faith 5
 5 We believe that a man must be ^acalled of God, by ^bprophecy, and by the laying on of ^chands by those who are in ^dauthority, to^epreach the Gospel and administer in the ^fordinances thereof.