Remember when Paladin crits heals would restore mana? they'd never run oom. I'm talking BC-ish.

Illumination: After getting a critical effect from your Flash of Light, Holy Light, or Holy Shock heal spell, gives you a X% chance to gain Mana equal to 30% of the base cost of your spell.

Level 40 Restoration shaman ability
While Water Shield is active, you recover mana when your direct healing spells have a critical effect. You regain X mana from a Healing Wave or Greater Healing Wave critical, X * 0.6 mana from a Healing Surge, Riptide, or Unleash Life critical, and X * 0.333 mana from a Chain Heal critical.