Saint Jean Vianney: 2.6: ...children, a servant may have a desire to fast, but he is obliged to pass the whole day …

Again, my children, a servant may have a desire to fast, but he is obliged to pass the whole day in digging and ploughing, or whatever you please. Well, if this servant is well instructed, he will think, "But if I do this, I shall not be able to satisfy my master. " Well, what will he do? He will eat his breakfast, and mortify himself in some other way. That is what we must do--we must always act in the way that will give most glory to the good God.