Fasting ought to be fulfilled not in abstinence of food only, but much more in cutting off vices. For when we submit ourselves to that discipline in order to withdraw that which is the nurse of carnal desires, there is no sort of good conscience more to be sought than that we should keep ourselves sober from unjust will, and abstinent from dishonourable action. This is an act of religion from which the sick are not excluded, seeing integrity of heart may be found in an infirm body.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: Serm. in Quadr., vi, 2