When is the best time for performing the Night Vigil Prayer (Qiyam al-Layl), what is the number of its rak'ahs, and must it conclude with Witr?

The time for night prayer begins after the 'Isha prayer and extends until the emergence of dawn. The best time for it is the last third of the night.

As for the number of its rak'ahs, it is open, based on the Prophet's (peace and blessings be upon him) saying: "The night prayer is two by two, and if one of you fears the coming of dawn, he should pray one rak'ah to make what he has prayed an odd number." It is preferable to limit it to eleven rak'ahs with Witr, because that was the prayer of the Prophet (peace and blessings be upon him) in Ramadan and other months, or thirteen rak'ahs, as reported by 'Aisha.

Concluding the night prayer with Witr is recommended, due to the Prophet's (peace and blessings be upon him) saying: "Make the last of your prayers at night Witr." It is also authentically reported that he (peace and blessings be upon him) sometimes prayed two rak'ahs after Witr while sitting.