Narrated Masruq: I asked Aisha about the night prayer of Allah's Apostle and she said, "It was seven, nine or eleven rak`at besides the two rak`at of the Fajr prayer (i.e. Sunna). "
Explanation & Benefits
Maulana Dawood Raz
Hadith Commentary:
By "the night prayer" is meant the prayer of Tahajjud (night vigil) outside of Ramadan, and Tarawih during Ramadan.
Source: Sahih Bukhari: Commentary by Maulana Dawood Raz, Page: 1139