This is the second condition for combining by delay.

For example, a traveller intends to combine by delay, but arrives in his hometown before the time of the first prayer has expired. In that case, he may not combine the first prayer with the second, because the excuse has ceased and no longer exists. He must therefore perform it within its time. This is an issue that confuses many people: many intend to combine by delay, then arrive in their hometown before the time of the first prayer expires and consequently do not pray it, thinking that they had intended to combine. This is mistaken. Rather, he must pray it within its time; then, when the time of the second prayer begins, he prays it—unless he is exhausted and finds it difficult to wait for the second prayer’s time to begin, because he needs to sleep, for example. In that case, he may combine because of hardship, not because of travel.

But should he pray it as four units or as two?

The answer is: he prays it as four units, because the effective cause for shortening the prayer is travel, and that has now ceased.

If he says, “Its time began while I was travelling, so it became obligatory upon me in its shortened form,”

we reply: Yes, it became obligatory upon you in its shortened form, because you were travelling; and now your liability remains occupied by it. Yet so long as it remains due from you, once you arrive in town it becomes obligatory upon you in its complete form. From this we know that the correct view is that if the time of a prayer begins while a person is in town, and he then travels before praying it, he may shorten it, because he has travelled while the prayer remains due from him, and a traveller shortens the prayer. Thus, according to the correct view, whether a prayer is shortened or not depends on the time of performing it, not on the time at which it became due. Therefore, if its time begins while you are travelling and you arrive in town before praying it, pray it as four units; and if its time begins while you are resident and you then travel, pray it as two units.