What is the ruling on one who prayed 'Ishā' a little before midnight, then the time for it expired while he was in the prayer?

The time for the Isha prayer does not expire until the Fajr (dawn) appears, according to the soundest opinion. One should hasten to perform the prayer at the beginning of its time. It is permissible to delay Isha until one-third or half of the night. So, whoever finds the strength to delay it, is not overcome by sleep, and does not cause hardship to any of the congregants, then delaying it is better for him. What is after midnight is considered a time of necessity, and prayer should not be delayed until the time of necessity without an excuse, except for those with excuses. If a person performs part of the prayer within the time and part of it outside due to an excuse, it is considered an اداء (performance within time). Scholars have differed on whether the prayer is considered اداء or قضاء (performance outside time) if part of it is performed within the time and part outside. The prayer of the mentioned person is valid.

As for whoever catches one rak'ah of the prayer before the time expires, he has caught it and completes it even if it is outside the time. Similarly, one who does not catch a rak'ah but has an excuse for the delay. As for one who does not catch a rak'ah and has no excuse for the delay, he has missed it, and some scholars have preponderated that he is not required to make it up.