But it is better to observe the fast with the intention of...

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).

Issue 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. Issue 1579: * If somebody is undecided in his niyyat whether to break or not an obligatory fixed fast, like that of Ramadhan, or decides to do so,…