(5) Establishing the Prayer and the Sunnah Regarding Them
كتاب إقامة الصلاة والسنة فيها
(171) Chapter: What was narrated concerning the (voluntary) night Prayer is two by two
(171) باب مَا جَاءَ فِي صَلاَةِ اللَّيْلِ رَكْعَتَيْنِ
Sunan Ibn Majah 1319 
It was narrated from Ibn ‘Umar that the Messenger of Allah (ﷺ) said:
“The night prayer is (to be offered) two by two.”
حَدَّثَنَا مُحَمَّدُ بْنُ رُمْحٍ، أَنْبَأَنَا اللَّيْثُ بْنُ سَعْدٍ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّ رَسُولَ اللَّهِ ـ صلى الله عليه وسلم ـ قَالَ ‏ "‏ صَلاَةُ اللَّيْلِ مَثْنَى مَثْنَى ‏"‏ ‏.‏
Grade :  Sahih (Darussalam)
Reference : Sunan Ibn Majah 1319
In-book reference : Book 5, Hadith 517
English translation : Vol. 1, Book 5, Hadith 1319