The Most Ancient Lives of Saint Patrick/The Life and Acts of St. Patrick/Chapter 18
Of his Fast continued for Twenty Days.
And all things succeeding prosperously, and their provision much abounding, these men soon forgot the Lord who had saved them from the straitness of hunger, and, ungrateful for the benefits extended unto them by the divine bounty, they sacrificed of their food to devils, and not unto God, imitating herein those Samaritans whom the Book of Kings records to have worshipped God, yet not to have the service of their idols. Wherefore it seemed good to Saint Patrick to eat no earthly food for twenty continual days, and, albeit he was much entreated thereto, he would in no wise join with them in their meals, lest he should appear to be contaminated with their sacrifices. And the power to endure this abstinence was given unto Patrick by the Lord, who had theretofore enabled Elias the prophet to fast forty days.