Historical Rules · 3 July 2020
Rule 702.58a
Official source text from the 3 July 2020 Rules release
Recover is a triggered ability that functions only while the card with recover is in a player’s graveyard. “Recover [cost]” means “When a creature is put into your graveyard from the battlefield, you may pay [cost]. If you do, return this card from your graveyard to your hand. Otherwise, exile this card.”