You mean this section
"Where a player commits an offence against an opponent within their own penalty area which denies an opponent an obvious goal-scoring opportunity and the referee awards a penalty kick, the offender is cautioned if the offence was an attempt to play the ball; in all other circumstances (e.g. holding, pulling, pushing, no possibility to play the ball etc.) the offending player must be sent off. A player, sent off player, substitute or substituted player who enters the field of play without the required refereeās permission and interferes with play or an opponent and denies the opposing team a goal or an obvious goal-scoring opportunity is guilty of a sending-off offence."
taken from the International FA Board who are responsible for the rules of Football
http://www.theifab.com/laws/fouls-and-misconduct/chapters/disciplinary-action