What is the end time of Isha prayer?

The Isha prayer time starts at the beginning of dawn when the time for Fajr prayer begins. However, it is frowned upon to delay the prayer without a legitimate reason past the first third of the night, and "night" in Islamic law means the time between the end of the Maghrib prayer and the start of the Fajr prayer. According to an opinion in the Maliki school, the prohibition is from delaying the prayer beyond the first half of the night, rather than just the first third.