While fasting and sitting on a certain mountain, and giving thanks to the Lord for all His dealings with me, I see the Shepherd sitting down beside me, and saying, “Why have you come hither [so] early in the morning?” “Because, sir,” I answered, “I have a station.” “What is a station?” he asked. “I am fasting, sir,” I replied. “What is this fasting,” he continued, “which you are observing?” “As I have been accustomed, sir,” I reply, “so I fast.” “You do not know,” he says, “how to fast unto the Lord: this useless fasting which you observe to Him is of no value.”
“Why, sir,” I answered, “do you say this?” “I say to you,” he continued, “that the fasting which you think you observe is not a fasting. But I will teach you what is a full and acceptable fasting to the Lord. Listen,” he continued: “God does not desire such an empty fasting. For fasting to God in this way you will do nothing for a righteous life; but offer to God a fasting of the following kind: Do no evil in your life, and serve the Lord with a pure heart: keep His commandments, walking in His precepts, and let no evil desire arise in your heart; and believe in God. If you do these things, and fear Him, and abstain from every evil thing, you will live unto God; and if you do these things, you will keep a great fast, and one acceptable before God.”
Source: The Pastor (or "The Shepherd") (New Advent)