Tahajjud prayer also known as qiyam is voluntary night prayer. It can be prayed anytime after Isha prayer up until the athan for Fajr prayer. It is not necessary to wake up from sleep to perform this prayer. The best time to perform it is the last third of the night. If a person is sure he'll perform the night prayer, it is recommended to not pray the witr prayer after Isha and instead end the night prayer with it but if he is not sure he can pray the witr with Isha and also pray the night praye

“Isha Prayer: More Rewarding Than Red Camels | Amazing Benefits of Witr”