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).
1586. If a person observing fast intentionally swallows something which remained in between his teeth, his fast is invalidated.
1589. There is no harm in swallowing one's phlegm or mucous from head and chest as long as it does not come upto one's mouth. However, if it reaches one's mouth, the obligatory precaution is that one should not swallow it.
1606. If a person observing fast wishes to quote something about which he has no authority or he does not know whether it is true or false, he should, as an obligatory precaution, give a reference of the person who reported it, or of the book in which it is written.
1615. As an obligatory precaution, a person who is observing fasts, should not allow the smoke of cigarettes, tobacco, and other similar things to reach his throat.
1622. If a fasting person falls into the water involuntarily, and his entire head goes into the water, or if he forgets that he is fasting and immerses his head in the water, his fast is not affected.
1641. If a person observing fast becomes Mohtalim during day time, it is not obligatory on him to do Ghusl at once.
1660. If a fasting person is certain that if he belches, something will come out from the throat, he should not, as a precaution, belch intentionally, but there is no harm in his belching if he is not certain about it.
1661. If a fasting person belches and something comes from his throat or into the mouth, he should throw it out, and if it is swallowed unintentionally, his fast is in order.