Fath al-Rabbani

Benefits: … Some people think that, just as there are four non-emphasized (ghayr mu’akkadah) Sunnah units before ‘Asr, there are also four non-emphasized Sunnah units before ‘Isha. However, their claim is without evidence. Rather, from general proofs, two units (rak‘ahs) before ‘Isha are established, as is this blessed hadith: ((There is no obligatory (fard) prayer except that before it are two units (rak‘ahs).)) (Sahih Ibn Hibban: 615, Sahihah: 232) That is, there is no obligatory prayer except that before it (at least) two units (of voluntary prayer) are prescribed. In this way, it becomes clear that before ‘Isha, at least two units should be performed. Yes, if there is time, then in light of other general narrations, voluntary (nafl) prayer may be offered, for which there is no fixed limit. As for the matter of the Sunnah units after the ‘Isha prayer, those units are established. It should be kept in mind that, like the other prayers, the total units of the ‘Isha prayer are six: four obligatory (fard) and two Sunnah. The Witr prayer is a night prayer; it is not a part of the ‘Isha prayer.

From general proofs, two units of prayer before both ‘Isha and Maghrib are established, but they cannot be counted among the fixed units of these prayers.