The stronger view in this issue is that he is not required to complete the prayer, because he began it in a state in which shortening was permissible, and he may therefore continue upon that basis. There is no clear evidence establishing the obligation to complete it.
“Or he remembers a prayer from residence while travelling, or the reverse; or he prays behind a resident, …”
This is the third issue. For example, a man is travelling and, during his journey, remembers that he did not pray the noon prayer while resident. He must pray four units, due to the Prophet’s saying, may Allah’s peace and blessings be upon him: “Whoever sleeps through a prayer or forgets it, let him pray it when he remembers it.” (1) That is, he should pray that prayer as it was when he remembers it. Moreover, this prayer became binding upon him as a complete prayer, so he must perform it as a complete prayer. This is clear.
His statement, “Or the reverse.”
This is the fourth issue. An example is a man who arrives in his hometown and then remembers that he did not pray the noon prayer while travelling. He must then pray four units, because it is a prayer that became obligatory for him while resident, so he is required to complete it. Also, shortening is a concession for travel, and his travel has now ended; therefore, he is required to complete it.
This is the position of the school. However, the stronger view is otherwise: if he remembers a prayer from travel while resident, he prays it shortened, due to the Prophet’s saying, may Allah’s peace and blessings be upon him: “Whoever sleeps through a prayer or forgets it, let him pray it when he remembers it”—that is, let him pray it as it was. This man remembers that he did not pray the noon prayer, which was two units in his case; thus, he is not required to complete it. We say, just as we said in the preceding case: this is a prayer that became obligatory for him while travelling, and a traveller’s prayer is shortened, so he is not required to complete it.
His statement, “Or he prays behind a resident.”