Sunan Ibn Majah Book 5, Hadith 1175

حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ الْمَلِكِ بْنِ أَبِي الشَّوَارِبِ، حَدَّثَنَا عَبْدُ الْوَاحِدِ بْنُ زِيَادٍ، حَدَّثَنَا عَاصِمٌ، عَنْ أَبِي مِجْلَزٍ، عَنِ ابْنِ عُمَرَ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ ‏"‏ صَلاَةُ اللَّيْلِ مَثْنَى مَثْنَى وَالْوِتْرُ رَكْعَةٌ ‏"‏ قُلْتُ أَرَأَيْتَ إِنْ غَلَبَتْنِي عَيْنِي أَرَأَيْتَ إِنْ نِمْتُ قَالَ اجْعَلْ أَرَأَيْتَ عِنْدَ ذَلِكَ النَّجْمِ ‏.‏ فَرَفَعْتُ رَأْسِي فَإِذَا السِّمَاكُ ثُمَّ أَعَادَ فَقَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ ‏"‏ صَلاَةُ اللَّيْلِ مَثْنَى مَثْنَى. وَالْوِتْرُ رَكْعَةٌ قَبْلَ الصُّبْحِ ‏"‏ ‏.‏

Abu Mijlaz narrated that Ibn ‘Umar said:“The Messenger of Allah (ﷺ) said: ‘Night prayers are to be offered two by two, and Witr is one Rak’ah.’ I said: ‘What do you think if I become drowsy and I want to sleep?’ He said: ‘Put “what do you think” up there with that star? (i.e., don’t think about it at all).’ I raised my head and saw As- Simak.* He repeated that the Messenger of Allah (ﷺ) said, ‘Night prayers are to be offered two by two, and Witr is one Rak’ah, before dawn.’” * Here, As-Simak refers to a star or stars, either Arcturus (As-Simak Ar-Ramih) or Spica, also called Alpha Virginis (As-Simak Al-A'zal)