- If a person did not know or forgot that it was the month of Ramadan, and takes notice of this before Zuhr and if he has performed some act which will invalidates a fast, his fast is void. But, he should not perform any act till Maghrib which invalidates a fast and should also observe qadha of that fast after Ramadan. The same rule applies if he learns after Zuhr that it is the month of Ramadan. But if he learns before Zuhr, and if he has not done anything which would invalidate his fast, his fast will be valid.
If a child reaches the age of puberty before the Adhan for Fajr prayers in the month of Ramadan he/she should keep fast and if he/she reaches the age of puberty after the Fajr Adhan, the fast of that day is not obligatory for him/her except if he/she intended to observe a Mustahab fast on that day, then he/she should complete it as a precaution.
- If a person who has been hired to observe the fasts of a dead person or has fasts of Kaffarah upon him as an obligation, observes Mustahab fasts, there is no harm in it. However, if a person has his own qadha of fasts, he cannot observe Mustahab fasts. If he forgets this and observes a Mustahab fast and remembers it before Zuhr his Mustahab fast will be void and he can convert his intention to the fast of qadha, and if he takes notice of the situation after Zuhr his fast is void as a precaution, and similarly if he remembers this after Maghrib, the validity of his fast is a matter if Ishkal.
- If it is obligatory for a person to observe a specific fast other than the fast of the month of Ramadan, for example, if he has vowed that he would observe fast on a particular day, and he does not make an intention purposely till the Adhan for Fajr prayers, his fast is void. And if he does not know that it is obligatory for him to fast on that day or forgets about it and remembers it before midday, and if he has not performed any act which invalidates the fast and makes an intention to fast, his fast is in order, and if he remembers after Zuhr, he should follow the precaution applied to the fast of Ramadan.
- If a person does not make an intention till near Zuhr for an obligatory fast which has no fixed time, like a fast of Kaffarah, there is no harm in it. In fact, if he had decided before making a niyyat that he would not fast, or was undecided as to whether he should or should not fast, if he has not performed any act which invalidates a fast, and decides before Zuhr to fast, his fast will be in order.
- If a non-Muslim embraces Islam in the month of Ramadan before Zuhr, he should, on the basis of obligatory precaution, make an intention to fast, and complete it provided that he had not committed any act which would make a fast void. And if he does not observe fast on that day he should give its qadha.
- If a patient recovers from his illness in the middle of a day in the month of Ramadan, before Zuhr, and if he has not done anything to invalidate the fast, he should make niyyat and fast. But if he recovers after Zuhr, it will not be obligatory on him to fast on that day.
If one doubts whether it is the last day of Sha’ban or the first day of Ramadan then the fast on that day is not obligatory. If however, somebody wants to observe fast on that day he cannot do so with the intention of observing the Ramadan fast, but if he makes an intention that if it is Ramadan then it is the Ramadan fast and if it is not Ramadan then it is qadha fast or some other fast like that, his fast will be valid. But it is better to observe the fast with the intention of qadha fast or some other fast, and if it is known later that it was Ramadan then it will automatically be Ramadan fast. And even if he makes a niyyat of a natural fast, and later it becomes known that it is Ramadan, it will be sufficient (i.e. that fast will be counted as the Ramadan fast).
- If it is doubtful whether it is the last day of Sha’ban or the first of Ramadan, and a person observes a qadha or a Mustahab fast or some other fast on that day, and later comes to know the same day that it is the first of Ramadan, then he should convert the intention to the Ramadan fast.
- If somebody is undecided in his niyyat whether to break or not an obligatory fixed fast, like that of Ramadan, or decides to do so, immediately his fast becomes invalid even if he does not actually break it or is repentant of his intention.
- If, while observing a Mustahab fast or an obligatory fast the time of which is not fixed (e.g. a fast for Kaffarah) a person intends to break the fast or wavers whether or not he should do so, and if he does not break it, he should make a fresh niyyat before Zuhr in the case of an obligatory fast, and before Maghrib in the case of a Mustahab fast. That way his fast will be in order.