Muwatta Malik 271

وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ عَائِشَةَ، زَوْجَ النَّبِيِّ صلى الله عليه وسلم كَانَتْ تَقُولُ مَنْ خَشِيَ أَنْ يَنَامَ حَتَّى يُصْبِحَ فَلْيُوتِرْ قَبْلَ أَنْ يَنَامَ وَمَنْ رَجَا أَنْ يَسْتَيْقِظَ آخِرَ اللَّيْلِ فَلْيُؤَخِّرْ وِتْرَهُ ‏.‏

Yahya related to me from Malik that he had heard that A'isha, the wife of the Prophet, may Allah bless him and grant him peace, used to say, "If someone fears that he will sleep through till the morning, let him pray the witr before he sleeps, and if some one hopes to wake for the last part of the night, let him delay his witr

Reference

Muwatta Malik 271

In-book

Book 7, Hadith 18