2Sam 23:17

“I do not fear the uncleanness of food but only the uncleanness of uncontrolled desire. I know that Noah was permitted to eat every kind of meat which was edible; that Elijah was nourished on meat; that John, endowed with a marvelous abstinence, was not made unclean by partaking of living things, namely, the locusts which happened to be available as food. And I know that Esau was led into error by his greed for lentils; that David blamed himself for his craving for water; and that our King was tempted not by flesh but by bread. Further, the people in the desert deserved to be reprimanded, not because they desired meat but because they murmured against the Lord as a result of this desire for meat. Having been placed among these temptations, then, I struggle daily against undisciplined desire in eating and drinking.”

“When long afterward David sat against the battle lines of enemies, he wished from desire to drink water from the cistern of Bethlehem. His chosen soldiers, breaking through the midst of the opposing forces, brought back unharmed the water the king had desired. But the man instructed by scourges immediately reproached himself for having desired water at the peril of his soldiers, and pouring it out, he offered it to the Lord, as it is written there: He poured it out to the Lord. For the water poured out was turned into a sacrifice to the Lord, because he slew the fault of concupiscence through the penance of his self-reproach. He therefore who once did not at all fear to covet another's wife, afterward was even afraid because he had coveted water. For since he remembered having perpetrated unlawful things, now stern against himself, he abstained even from lawful things. Thus, thus do we do penance, if we perfectly bewail what we have committed.”