Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) narrated that the Messenger of Allah (peace and blessings be upon him) was asked about Witr, so he (peace and blessings be upon him) said: "Pray Witr before Fajr."
Hadith Referenceسنن دارمي / من كتاب الصللاة / 1627
(Commentary on Hadith 1626) From this hadith, the last time for Witr is known, which is until before the rising of Fajr. If one is unable to perform it at that time, then it can be made up (qada) after sunrise until before Dhuhr, but instead of one rak‘ah, two rak‘ahs must be performed, as is established from the Messenger of Allah sallallahu alayhi wa sallam. On one occasion, he sallallahu alayhi wa sallam was unable to perform Witr at night, so he prayed twelve rak‘ahs during the day, that is, twelve instead of eleven. Its details have already passed in Hadith number (1514).