When this Pokémon is affected by burn, paralysis, poison, or sleep, its Attack is increased by 50%. Guts ignores burn's Attack drop.
http://www.smogon.com/dp/abilities/guts
Guts raises the Attack stat by 50% while affected by the Burn, Paralysis, or Poison status ailments. The Attack drop from Burn does not occur. In Generation IV, the Attack stat is also raised by the Sleep status ailment, even self-induced sleep.
http://bulbapedia.bulbagarden.net/wiki/Guts
There ya go. 2 differen't sources.
http://www.smogon.com/dp/abilities/guts
Guts raises the Attack stat by 50% while affected by the Burn, Paralysis, or Poison status ailments. The Attack drop from Burn does not occur. In Generation IV, the Attack stat is also raised by the Sleep status ailment, even self-induced sleep.
http://bulbapedia.bulbagarden.net/wiki/Guts
There ya go. 2 differen't sources.