Is it permissible to postpone the two rak'ahs after 'Isha' prayer, or four rak'ahs as reported from some Companions like 'Abdullah ibn 'Amr, 'Aisha, and 'Abdullah ibn Mas'ud - may Allah be pleased with them - until the last third of the night?

The preferred time for the two rak'ahs after 'Isha' is from after 'Isha' until midnight, and the time of necessity extends until Fajr. As for the four rak'ahs after 'Isha', there is no restriction on their time. They include what is immediately after 'Isha' or after a pause, and they are considered part of the night prayer. Furthermore, the hadiths that restrict their performance to the mosque are not authentic. Al-Shawkani said: "Most of the hadiths indicate that this was done at home, and there is no mention of restriction to the mosque." Therefore, whenever these rak'ahs are prayed during the night, there is hope of receiving the reward.