The Institutes, Book 8
Anger That Outlasts the Sunset
But what am I to say of those, and I cannot say it without shame of my own, whose unforgiving temper not even the going down of the sun can bring to an end? They draw it out for several days and nurse bitter feelings against those who provoked them. In words they say they are not angry, but in fact and deed they show that they are extremely disturbed. For they do not speak to them pleasantly or address them with ordinary courtesy, and they think they are doing no wrong in this, because they do not seek revenge for what upset them. But since they either do not dare, or at any rate are not able, to show their anger openly and give way to it, they drive the poison of anger inward, to their own harm. They cherish it secretly in their hearts and feed on it silently within themselves. They do not shake off their sulky mood by an effort of mind, but digest it as the days go by, and soften it somewhat after a while.