Serenity

You regularly spend time in meditation, maintaining peace of mind and a tranquil spirit. Choose one of the following ability scores: Wisdom, Charisma, or Sanity. You gain the following benefits

• Increase the value of the chosen ability score by 1 to a maximum of 20.
• You gain proficiency in saving throws for the chosen ability score.
• Once per long rest, when you would be subjected to an effect resulting in short or long term madness , you can choose to be afflicted for the minimum amount of time required (1 minute for short term madness, 1 hour for long term madness). 

Sanity (Dungeon Master's Guide page 265)

Madness (Dungeon Master's Guide page 259)