Why is the Fajr prayer not combined with the 'Isha' prayer?

The questioner : Yes. And the rule, and the rule from the hardship, and how the Fajr prayer was excluded from the congregation. Yes.

The Shaykh : Yes, he says, may Allah guide you, if the cause is hardship, why was the Fajr prayer excluded from the Friday prayer? The answer is easy, may Allah guide you: the Fajr prayer is independent in its time, it stands alone, so we cannot combine it, because if we delayed the 'Isha' prayer to it, there would be a time between it and the 'Isha' prayer that is not a time for either of them.

The questioner : Likewise after it exits.

The Shaykh : And likewise between the 'Asr and the Maghrib. Yes, because the 'Asr is of a different type than the Maghrib. Clear. And likewise between the Zuhr and the 'Asr, for the time between them, and not for the time of the Fajr or the Zuhr.