How does one pray Qiyam al-Layl after performing the Witr prayer before sleep?

He who is confident that he will rise in the latter part of the night, it is better for him to delay Witr until then. And he who fears he will not rise, let him pray Witr before he sleeps, due to the saying of the Prophet, peace and blessings be upon him: "Whoever among you fears that he will not rise in the latter part of the night, let him pray Witr and then sleep. And whoever is confident of rising in the latter part of the night, let him pray Witr at its end, for indeed, the recitation at the end of the night is witnessed, and that is better."

If a Muslim prays Witr at the beginning of the night and then rises for Tahajjud, it is recommended for him to pray as many rak'ahs as he wishes, in sets of two, and not to nullify his first Witr. This is because prayer after Witr is permissible, and it has been established that the Prophet, peace and blessings be upon him, used to pray two rak'ahs after Witr while sitting.

And whoever sleeps through his Witr until dawn breaks, it is legislated for him to make it up, due to his (peace and blessings be upon him) saying: "Whoever sleeps through his Witr at night, let him make it up during the day." Some scholars have held that he makes it up during the day as an even number of rak'ahs.