Sahih Bukhari
Prayer at Night (Tahajjud)
Volume: 002 / Book Number: 021 / Hadith Number: 258
Narrated 'Aisha :
After offering the Sunna of the Fajr prayer, the Prophet used to talk to me, if I happen to be awake; otherwise he would lie down till the Iqama call was proclaimed (for the Fajr prayer).