Greater Endurance (3.5e Feat)
From D&D Wiki
Greater Endurance [General]
<!-A short summary of the feat->
Benefit: You gain a total of +6 bonus on the following checks and saves: Swim checks made to resist nonlethal damage, Constitution checks made to continue running, Constitution checks made to avoid nonlethal damage from a forced march, Constitution checks made to hold your breath, Constitution checks made to avoid nonlethal damage from starvation or thirst, Fortitude saves made to avoid nonlethal damage from hot or cold environments, and Fortitude saves made to resist damage from suffocation. Also, you may sleep in light, medium and heavy armor without becoming fatigued.
Normal: A character without this feat who sleeps in medium or heavier armor is automatically fatigued the next day.