Why is it not permissible to perform the Duha prayer (Salat al-Ishraq) before the Eid prayer, if the Prophet, peace and blessings be upon him, used to pray it every day, knowing that the time for the Duha prayer is after sunrise, and voluntary prayers are prohibited before the Eid prayer, whether in the mosque or at home?

Ishraq prayer consists of two rak'ahs performed after sunrise and after the time of prohibition has passed. It is considered a part of the Duha prayer, at its earliest time. There is no evidence that the Prophet, peace be upon him, performed it daily, but there are narrations describing his daytime prayers, among them a prayer of two rak'ahs when the sun had risen after its appearance, which some call Ishraq prayer.

As for reconciling Ishraq prayer with the Prophet's not praying before Eid, this can be understood in several ways: 1. The narrations negating prayer before Eid apply only to the Eid prayer ground, and not to voluntary prayers performed at home or in the mosque. 2. The Prophet, peace be upon him, used to hasten to the Eid prayer, and his time during Ishraq was dedicated to preparing for it and going to it. 3. The Eid prayer may suffice for the two rak'ahs of Ishraq prayer, as it achieves its purpose, which is to occupy the time with the remembrance of Allah.

Based on this, it is permissible for a Muslim to perform the Ishraq prayer at home or in their mosque before going to the Eid prayer, or to suffice with the Eid prayer itself.