Masruq narrates from Aishah (may Allah be pleased with her) that he (peace and blessings be upon him) prayed witr in every part of the night: in its early part, its middle part and its last part; and the latest time of his (peace and blessings be upon him) witr reached the pre-dawn (sahar).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4835