Riyad as-Salihin, Book 9, Hadith 1138 (In-Book) ⓘ

Jabir (May Allah be pleased with him)reported: The Messenger of Allah said, "He who apprehends that he may not get up in the later part of the night, should observe the Witr prayer in the first part of it; and he who is certain to get up in the last part of it, he should observe Witr at the end of the night, because Salat at the end of the night is attended (by the angels), and that is better."[Muslim].

وعن جابر رضي الله عنه قال قال رسول الله صلى الله عليه وسلم ‏:‏ ‏ "‏من خاف أن لا يقوم الليل فليوتر أوله، ومن طمع أن يقوم آخره، فليوتر آخر الليل، فإن صلاة آخر الليل مشهودة، وذلك أفضل‏" ‏‏.‏ ‏(‏‏(‏رواه مسلم‏)‏‏)‏‏.‏