Is it permissible to perform the Sunnah (supererogatory prayer) of Isha before the obligatory prayer, and what is the ruling on one who did so out of ignorance of the ruling?

The regular (Sunan Rawatib) supererogatory prayers are of two types: pre-Fard (Qabliyyah), which are prayed before the obligatory prayer, and their time extends from the beginning of the prayer's prescribed time until one starts the obligatory prayer; and post-Fard (Ba'diyyah), which are prayed after the obligatory prayer, and their time extends from finishing the obligatory prayer until the time for that obligatory prayer ends. So, if someone prays the post-Isha Sunnah (definition) before the Isha (obligatory prayer), it is not counted as a regular supererogatory Sunnah but rather as a general voluntary prayer, because it was performed before its prescribed time. However, for someone who did this out of ignorance, there is hope for him to receive the reward of the Sunnah.