Urwah bin al-Zubayr narrates: Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) would pray the Witr after the true dawn had broken, and my father (Sayyiduna al-Zubayr bin al-Awwam, may Allah be pleased with him) would pray the Witr before the true dawn.
Al-Tabarani recorded it in al-Mu'jam al-Kabir, and its narrators have been declared trustworthy.