How can one combine the Witr prayer and Tahajjud, and is Tahajjud performed before or after Witr?

"Qiyam" is spending the night, even if for an hour, in acts of worship. "Tahajjud" is the night prayer, and the correct view is that it refers to any night prayer. The night prayer is performed two rak'ahs at a time, concluding with a single rak'ah of Witr. The Sunnah is to pray two rak'ahs at a time, to begin with Tahajjud first, and for Witr to be the last prayer of the night, with all of this occurring before the dawn adhan. A Muslim may pray as much as they wish during the night, from after the 'Isha prayer until Fajr, and the best times for night prayer are its latter parts. If one prays in the early part of the night and performs Witr, and then wishes to pray in the latter part of the night, they may pray as much as they wish, two rak'ahs at a time, without repeating Witr.