Sahih Muslim
Sahih Muslim 755 b
One who fears that he will not get up at the end of the night, then he should pray Witr at the beginning of the night
Arabic hadith text
وَحَدَّثَنِي سَلَمَةُ بْنُ شَبِيبٍ، حَدَّثَنَا الْحَسَنُ بْنُ أَعْيَنَ، حَدَّثَنَا مَعْقِلٌ، - وَهُوَ ابْنُ عُبَيْدِ اللَّهِ - عَنْ أَبِي الزُّبَيْرِ، عَنْ جَابِرٍ، قَالَ سَمِعْتُ النَّبِيَّ صلى الله عليه وسلم يَقُولُ "أَيُّكُمْ خَافَ أَنْ لاَ يَقُومَ مِنْ آخِرِ اللَّيْلِ فَلْيُوتِرْ ثُمَّ لْيَرْقُدْ وَمَنْ وَثِقَ بِقِيَامٍ مِنَ اللَّيْلِ فَلْيُوتِرْ مِنْ آخِرِهِ فَإِنَّ قِرَاءَةَ آخِرِ اللَّيْلِ مَحْضُورَةٌ وَذَلِكَ أَفْضَلُ "
Translation
Jabir reported Allah's Messenger (ﷺ) as saying
He who amongst you is afraid that he may not be able to get up at the end of the night should observe Witr (in the first part) and then sleep, and he who is confident of getting up and praying at night (i. e. Tahajjud prayer) should observe it at the end of it, for the recitation at the end of the night is witnessed*, and that is better.*: meaning, "by angels" (Sharh an-Nawawi)