There is another view on this matter: witr is not to be made up. This is one report from Ahmad, based on the report that the Prophet said:

“When dawn breaks, the time for night prayer and witr has passed.”

Those who hold this view say that witr is intended to be the final act of worship at night, just as Maghrib is the odd-numbered prayer concluding the day’s worship. This is why, when the Prophet, may Allah bless him and grant him peace, missed his night prayers, he would pray twelve rak‘ahs during the day. Had witr been included among them, they would have been thirteen rak‘ahs.

The correct view is that witr is to be made up before the Fajr prayer. Once that prayer has been performed, making up witr no longer serves the purpose for which it was prescribed. Allah knows best.

Shaykh al-Islām was asked about a Shāfi‘ī imam who leads a congregation of Hanafīs and Shāfi‘īs, with the Hanafīs praying separately when it comes to witr.

He replied:

It is established in the two Sahīh collections that the Prophet, may Allah bless him and grant him peace, said:

“Night prayer is offered two rak‘ahs at a time. If you fear that dawn is approaching, pray one rak‘ah to make what you have prayed odd-numbered.”

It is also established in the Sahīh that the Prophet, may Allah bless him and grant him peace, would pray witr as a single rak‘ah separate from those preceding it, and that he would pray witr as five or seven rak‘ahs, giving the salām only at the end.