works of supererogation

from The Collaborative International Dictionary of English v.0.48

Supererogation \Su`per*er`o*ga"tion\, n. [L. supererogatio a
   payment in addition.]
   The act of supererogating; performance of more than duty or
   necessity requires.
   [1913 Webster]

   {Works of supererogation} (R. C. Ch.), those good deeds
      believed to have been performed by saints, or capable of
      being performed by men, over and above what is required
      for their own salvation.
      [1913 Webster]