Historical Rules · 10 August 2018
Rule 702.52a
Official source text from the 10 August 2018 Rules release
Transmute is an activated ability that functions only while the card with transmute is in a player’s hand. “Transmute [cost]” means “[Cost], Discard this card: Search your library for a card with the same converted mana cost as the discarded card, reveal that card, and put it into your hand. Then shuffle your library. Activate this ability only any time you could cast a sorcery.”