Night Prayer
Qiyam ul Layl — the night prayer — is one of the most virtuous voluntary acts of worship in Islam.
Qiyam ul Layl literally means "standing in the night." It refers to voluntary prayers performed after Isha and before Fajr. Tahajjud specifically refers to the prayer performed after sleeping and waking up. Allah says: "And during part of the night, rise from sleep for additional worship." (Al-Isra 17:79)
The Prophet said: "The best prayer after the obligatory prayers is the night prayer." (Sahih Muslim). The last third of the night is the most blessed time — Allah descends to the lowest heaven and asks: "Who is calling upon Me that I may answer? Who is asking of Me that I may give? Who is seeking My forgiveness that I may forgive?"
There is no fixed maximum. The Prophet typically prayed 8 Rakats of Tahajjud plus 3 Witr. The minimum is 2 Rakats. Each pair of Rakats is followed by Tasleem. Longer Surahs and longer Sujood are encouraged. End with Witr if not already prayed.
Any Surah may be recited. The Prophet was known to recite Surah Al-Baqarah, Al-Imran, and An-Nisa in single Rakats. Shorter Surahs recited with Khushu (concentration) are better than long recitation with a distracted heart.