Sayyiduna Uqbah bin Amr and Sayyiduna Abu Musa al-Ash'ari (may Allah be pleased with them both) both said: the Messenger of Allah (peace and blessings be upon him) would pray witr sometimes at the beginning of the night and sometimes in the middle, so that there would be latitude for the Muslims.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14753