Thauban reported the Prophet (ﷺ) as saying, “This wakefulness is a toil and a burden, so when one of you observes a <i>witr</i> he should pray two <i>rak'as</i>. If he gets up during the night, well and good; otherwise they will serve for him." Tirmidhi transmitted it.

وَعَنْ ثَوْبَانَ عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «إِنَّ هَذَا السَّهَرَ جُهْدٌ وَثِقَلٌ فَإِذَا أَوْتَرَ أَحَدُكُمْ فَلْيَرْكَعْ رَكْعَتَيْنِ فَإِنْ قَامَ مِنَ اللَّيْلِ وَإِلَّا كَانَتَا لَهُ» . رَوَاهُ الدَّارِمِيُّ