عَنِ ابْنِ عُمَرَ رَضِيَ اللَّهُ عَنْهُ أَنَّهُ كَانَ إِذَا سُئِلَ عَنِ الْوِتْرِ، قَالَ: أَمَّا أَنَا فَلَوْ أَوْتَرْتُ قَبْلَ أَنْ أَنَامَ ثُمَّ أَرَدْتُّ أَنْ أُصَلِّيَ بِاللَّيْلِ شَفَعْتُ بِوَاحِدَةٍ مَا مَضَى مِنْ وَتْرِي ثُمَّ صَلَّيْتُ مَثْنَى مَثْنَى فَإِذَا قَضَيْتُ صَلَاتِي أَوْتَرْتُ بِوَاحِدَةٍ، إِنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ أَمَرَ أَنْ يُجْعَلَ آخِرَ صَلَاةِ اللَّيْلِ الْوِتْرُ
It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with him) that when he was asked about Witr, he would say: As far as I am concerned, if I perform Witr before sleeping, but then intend to pray at night, I perform one rak‘ah to make the previous Witr even, then I continue to pray two rak‘ahs at a time, and when I have completed the desired prayers, I perform one Witr at the end, because the Messenger of Allah (peace and blessings be upon him) commanded that Witr should be made the last prayer of the night.