How do we know that God has accepted our fasting?

The servant cannot know if his deed has been accepted, for Allah bestows His favor upon whom He wills. This is based on the Prophet's (PBUH) saying: "No one's deeds will admit him to Paradise, except that Allah covers me with favor and mercy." Thus, righteous deeds are a cause for entering Paradise, but they do not obligate anything. Success in performing righteous deeds and sincerity in them come through Allah's favor and mercy. Among the signs of acceptance of a deed is that the servant is guided to perform another righteous deed afterwards and remains steadfast upon it.