What is the ruling on changing one's practice based on one of the sayings of the scholars, and what is the ruling on the prayers performed based on the previous or subsequent fatwa?

The time for the Isha prayer extends until the appearance of dawn according to the majority of scholars. However, after the first third or half of the night, it becomes a time of necessity. The opinion that the Isha prayer performed after midnight is considered a missed prayer (qada’) is weak and contradicts the evidence and the fatwas of the Companions. Thus, the time after midnight is indeed a time for Isha, even if it is a time of permissibility or necessity. As for the intention to pray it as a missed prayer (qada’), it does not cause any harm.