Gregory the Dialogist

But David, who had taken to himself another man's wife, and had been sorely scourged for his fault, desired long afterwards to drink water from the cistern of Bethlehem; which when his bravest soldiers had brought to him, he refused to drink it, and poured it out as a libation to the Lord. For it was lawful for him to drink it, had he been so minded; but, because he remembered having done what was unlawful, he laudably abstained even from what was lawful. …

Register of Epistles, Book 11, Epistle 45 ↗