According to a hadith, once two people were fasting. While fasting, they sat together and began to speak ill of others. Although they were fasting, they indulged in backbiting. 
The Prophet said about them: "They began their fast by eating what is lawful, but broke their fast with what is unlawful." Here, by 'lawful' is meant food and water, but later because the two began to speak ill of others, this act broke their fast. Fasting, practiced only as a ritual, has no value at all. If a person does not observe fasting in its true spirit, then his fasting is merely hunger and thirst. Such a person will get nothing from his fasting, except hunger and thirst. (Sunan Ibn Majah 1690) He will only experience hunger and thirst. If a person observes fasting with its real spirit, then his fasting will be true. The spirit of fasting, or any action, is never temporary. Only the form of an action is temporary. Namaz has a form which observed five times a day, but this form is temporary. 

The spirit of Namaz is remembrance of God. This can never be temporary, rather it should be permanent. If observe the ground, you will remember God. If you observe the sky, you will remember God. If you see the sun, you will remember God. If you see the trees, you will remember God. If you see the mountains, then too you will remember God. Remembrance of God can never be temporary. Any kind of worship can be temporary only in terms of its form, but as far as the spirit is concerned, it should be everlasting and permanent. It will have its effects throughout one's life.  When a person observes such kind of fasting, this is really true fasting. Every person has two angels accompanying him. 
The Quran says: "The two recording angels are recording, sitting on the right and the left." (50:17)

Every person, man and woman, has two angels who are constantly making a record of his or her actions. What are these actions? One's intention, thoughts, behaviour, speech are all part of one's actions. One's intention is also part of one's action. One's dealings with others also part of one's actions.
The angels are recording all of one's actions. After death on the Day of Judgment, these angels will present the record of every human being before God Almighty, the Judge.If God affirms that a person's fasting was true or sincere, then alone will his fasting be accepted. A person's own understanding will not make his fasting acceptable to God.