1559. 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 Maghrib, 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 Adhan for Fajr prayers, and continue to refrain for some time after sunset from acts which invalidate a fast.
1560. 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.
1577. If one doubts whether it is the last day of Sha'ban or the first day of Ramadhan 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 Ramadhan fast, but if he makes an intention that if it is Ramadhan then it is the Ramadhan fast and if it is not Ramadhan 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 Ramadhan then it will automatically be Ramadhan fast. And even if he makes a niyyat of a natural fast, and later it becomes known that it is Ramadhan, it will be sufficient (i.e. that fast will be counted as the Ramadhan fast).
1578. If it is doubtful whether it is the last day of Sha'ban or the first of Ramadhan, 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 Ramadhan, then he should convert the intention to the Ramadhan fast.
And in order to ensure that he has been fasting throughout this time he should begin abstaining earlier than the Adhan for Fajr prayers, and continue to refrain for some time after sunset from acts which invalidate a fast.
1560. 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.
1577. If one doubts whether it is the last day of Sha'ban or the first day of Ramadhan 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 Ramadhan fast, but if he makes an intention that if it is Ramadhan then it is the Ramadhan fast and if it is not Ramadhan 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 Ramadhan then it will automatically be Ramadhan fast. And even if he makes a niyyat of a natural fast, and later it becomes known that it is Ramadhan, it will be sufficient (i.e. that fast will be counted as the Ramadhan fast).
1578. If it is doubtful whether it is the last day of Sha'ban or the first of Ramadhan, 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 Ramadhan, then he should convert the intention to the Ramadhan fast.