Mukhtasar Muslim

Sayyiduna Jabir (may Allah be pleased with him) reports that the Messenger of Allah (peace and blessings be upon him) said: Whoever fears that he may not be able to get up at the end of the night should perform Witr in the early part of the night (after ‘Isha). And whoever hopes to get up at the end of the night should perform Witr at the end of the night, because the prayer at night is such that angels are present in it, and it is superior.