Historical Rules · 7 August 2020
Rule 702.51a
Official source text from the 7 August 2020 Rules release
Dredge is a static ability that functions only while the card with dredge is in a player’s graveyard. “Dredge N” means “As long as you have at least N cards in your library, if you would draw a card, you may instead mill N cards and return this card from your graveyard to your hand.”