What is the recommended practice for a person who prayed Witr (odd number of rak'ahs) at the beginning of the night and then wakes up for Tahajjud (night vigil)?
Chapter on the Times When Prayer is Prohibited
Al-Mughni
Book of Prayer
Primary text
It is recommended that one prays in sets of two rak'ahs and does not break the initial Witr prayer. This view is held by Abu Bakr As-Siddiq, Ammar, Sa'd ibn Abi Waqqas, 'A'idh ibn 'Amr, Ibn Abbas, Abu Hurairah, and Aisha. Alqamah also did not permit breaking the Witr. This is the position of Tawus, Abu Mijlaz, An-Nakhai, Malik, Al-Awza'i, and Abu Thawr. Imam Ahmad indicated that he hopes for anyone who adopts this view, as a group of scholars practiced it. The interpretation is that if one wakes for Tahajjud, they pray one rak'ah to make the first Witr an even number (Shafa'), then pray in sets of two, and then make the final rak'ah of their Tahajjud session Witr.
Supporting text
There is an opposing view, attributed to Ali, Usamah, Abu Hurairah, Umar, Uthman, Sa'd, Ibn Umar, Ibn Abbas, and Ibn Mas'ud, which is also the position of Ishaq. This view suggests that one should break the Witr prayer. This is supported by the saying of the Prophet (peace be upon him): "Make the last of your prayers at night an odd number (Witr)."