Is it permissible to begin the qiyam al-layl prayer—that is, the Tarawih prayer—between the adhan for isha and its iqamah?

The time for Qiyam al-Layl begins after the 'Isha prayer. Prayer before 'Isha is not considered Qiyam al-Layl. However, prayer between the adhan and iqama is encouraged, as is supererogatory prayer between Maghrib and 'Isha. It has been said that this is the "nashiyat al-layl" mentioned in Surah Al-Muzzammil. Voluntary prayer at this time is encouraged, and the one who prays it is rewarded. If the worshipper performs Witr with the Imam, there is no harm in performing supererogatory prayers afterward without repeating Witr.