Whoever sleeps and fails to recite his nightly portion, or part of it, and then recites it…

Hizb means part of something, like the Hizbs (parts) of the Qur’an. So if one is used to performing the (voluntary) prayer during the night, but he falls asleep and misses it completely or partially, and he then makes up for it between the Fajr prayer and the Zhuhr prayer, it will be as if he prayed it during that night. However, if one is used to perform Witr prayer at night, he must not perform it during the day in case he makes up for what he missed at night. Rather, he should add another Rak‘ah to the Witr. In other words, if he usually prays three Rak‘ahs as Witr, then he should make it four, or if he usually prays five, then let him make it six, and so on. The evidence for this is the Hadīth of ‘Ā’ishah (may Allah be pleased with her) who related that the Prophet (may Allah's peace and blessings be upon him) when he was overcome by sleep or pain during the night, would pray twelve Rak‘ahs during the day. It should be noted that making up (for the missed night prayer) should be done after the sun has risen and has reached the height of a spear's length in order to avoid praying during the time that this is forbidden.