May Allah bless you all. I have a question, is it permissible to delay the Sunnah of Isha prayer until tahajjud and pray it then? Also, what is the ruling if one forgets to offer a sunnah prayer and then remembers it later?
The most recommended is to pray the Sunnah of Ishaa prayer in its time, which is after ishaa prayer, but if you forgot it and at-tahajjud time entered, then you have to pray it before to pray at-tahajjud.
As for the Sunnah prayer which you forgot, you pray it as soon as you remember it.