What is the delaying the Isha Prayer to a late time?
The best act with respect to the Isha Prayer is to delay it until its last time. Whatever amount it is delayed is better. This is true except in the case of men. If a man is going to delay the Isha Prayer and by so doing is going to miss performing it in congregation, then it is not allowed for him to delay it and miss the congregation. As for women in their homes, the more they delay the Isha Prayer, the better for them. However, they cannot delay it beyond half of the night.
Shaikh ibn Uthaimin