The prohibition of going to bed before 'Isha' prayer is that if one sleeps late at night, it becomes difficult for him to get up for Tahajjud prayer or Fajr prayer. Moreover, if a person goes to sleep soon after 'Isha' prayer, all his activities of the day will end at 'Isha', which is the most meritorious act. It should also be borne in mind that when holding a conversation which is disliked or forbidden at other times becomes even more so at this particular time (i.e., after 'Isha' prayer). Imam An-Nawawi's contention that things like academic discussion, talking to a guest, discussing the lives of the pious etc., are not only permissible but desirable, is also subject to the condition that such an activity does not involve the risk of losing the Fajr prayer. If one spends so much time in such activities that he is likely to miss the Fajr prayer, then the permission to hold academic discussion becomes doubtful.