In this rule

Historical Rules · 15 February 2021

Rule 305.2b

Official source text from the 15 February 2021 Rules release

Permalink

A player can’t play a land, for any reason, if the number of lands the player can play this turn is equal to or less than the number of lands they have already played this turn. Ignore any part of an effect that instructs a player to do so.

Find this number in the current Rules