NIYYAT FOR FASTING.

1. Fasting means that a person must, in obedience to the commands of Allah, from the time of adhan for fajr prayers up to the time of adhan for maghrib prayers, avoid nine things which will be mentioned later.
2. It is not necessary for a person to pass the niyyat for fasting through his mind or to say that he would be fasting on the following day. In fact, it is sufficient for him to decide that in obedience to the command of Allah he will not perform from the time of adhan for fajr prayers up to the time of adhan for maghrib prayers, any act which may invalidate the fast. And in order to ensure that he has been fasting throughout this time he should begin abstaining earlier than the time of adhan for fajr prayers, and continue to refrain for some time after the adhan for maghrib prayers from acts which invalidate a fast.
3. A person can make niyyat every night of the holy month of Ramadhan that he would be fasting on the following day, and it is better to make niyyat on the first night of Ramadhan that he would fast throughout that month.
4. The last time for making niyyat to observe a fast of Ramadhan for a conscious person, is moments before the time of adhan for fajr prayers.
5. If a person sleeps before the time for fajr prayers in Ramadhan without making a niyyat, and wakes up before zuhr to make a niyyat of fast, his fast will be in order. But if he wakes up after Zuhr, as a precaution, he should continue with the abstinence with the niyyat of qurbat and then give its qadha’ also.
6. If a person makes a niyyat before the time of Adhan for Fajr prayers to observe a fast, and then goes to sleep, and wakes up after Maghrib his fast is in order.
7. If a child reaches the age of puberty before the time of adhan for fajr prayers in the month of Ramadhan he/she should keep fast, and if he/she reaches the age puberty after the adhan for fajr prayers, the fast on that day is not obligatory for him/her.
8. If a patient recovers from his illness before zuhr in the month of Ramadhan, 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.
9. If one doubts whether it is the last day of Sha’baan or the first day of Ramadhan then the fast on that day is not obligatory. However, if one wants to fast on that day, 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 Ramadhan then it will automatically be Ramadhan fast. And if he learns on the same day before maghrib that it is the first day of Ramadhan, then he should convert the intention to the Ramadhan fast.
10. If somebody is undecided in his niyyat whether to break the fast or not, or decides to do so, immediately his fast becomes invalid even if he does not actually break it or is repentant of his intention.

According to FATAWA of Ayatullah Al-Uzma Seyyid Ali-Husaini Seestani