1662. If a person intentionally and voluntarily commits an act which invalidates fast, his fast becomes void, but if he does not commit such an act intentionally, there is no harm in it (i.e. his fast is valid). However, if a person in Janabat sleeps and does not do Ghusl till the time of Fajr prayers, as detailed in rule no. 1639, his fast is void. Similarly, if a person due to utter ignorance of the rule that a certain act will invalidate the fast, or due to reliance upon some authority which he thought was genuine, unhesitatingly commits an act which invalidates the fast, his fast will not be void, except in the cases of eating, drinking and sexual intercourse.
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