Abu Dawud Book 2, Hadith Number 1356.

Chapter : On the number of rakahs of the prayer at night.

Narated By ‘Aisha : The Apostle of Allah (PBUH) offered the night prayer and then prayed eight rak’ahs standing, and two rak’ahs between the two adhans (i.e. the adhan for the dawn prayer and the iqamah). He never left them.

Ja’far b. Musafir said in his version: (He prayed) two rak’ahs sitting between the two adhans. He added the word “sitting.”