Hadith: A man asked the Prophet (ﷺ) while he was on the pulpit: What do you say about the night prayer? He (ﷺ) said: "Two by two

عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ رَضيَ اللهُ عنهما:
سَأَلَ رَجُلٌ النَّبِيَّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ وَهُوَ عَلَى المِنْبَرِ، مَا تَرَى فِي صَلاَةِ اللَّيْلِ، قَالَ: «مَثْنَى مَثْنَى، فَإِذَا خَشِيَ الصُّبْحَ صَلَّى وَاحِدَةً، فَأَوْتَرَتْ لَهُ مَا صَلَّى» وَإِنَّهُ كَانَ يَقُولُ: «اجْعَلُوا آخِرَ صَلاَتِكُمْ وِتْرًا» فَإِنَّ النَّبِيَّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ أَمَرَ بِهِ.
[صحيح] - [متفق عليه] - [صحيح البخاري: 472]

‘Abdullah ibn ‘Umar (may Allah be pleased with him and his father) reported:
A man asked the Prophet (ﷺ) while he was on the pulpit: What do you say about the night prayer? He (ﷺ) said: "Two by two (i.e., in sets of two Rak‘ahs). When he fears that dawn is approaching, he should pray one (Rak‘ah), which will make what he has prayed Witr (odd)." And he (ﷺ) used to say: "Make the last of your prayers at night Witr,” for the Prophet (ﷺ) commanded it.
[Authentic hadith] - [Narrated by Bukhari & Muslim] - [Sahih Bukhari - 472]

Explanation

A man asked the Prophet (ﷺ) while he was delivering a sermon on the pulpit: O Messenger of Allah, teach me how to perform the night prayer. The Prophet (ﷺ) said: Pray and make Taslīm after every two Rak‘ahs. When you fear that dawn is near, then pray one Rak‘ah, which will make what you have prayed Witr. And he (ﷺ) used to advise making Witr the last prayer of the night.

Benefits from the Hadith

1. The basic rule for night prayer is to make Taslīm after every two Rak‘ahs, except for the Witr prayer.
2. The night prayer is not limited to a specific number of Rak‘ahs, as indicated by the unrestricted wording of the text.
3. An-Nawawi said: The Hadīth "the prayer of the night and day is two by two" refers to what is preferable—that one makes Taslīm after every two Rak‘ahs. This applies to both the voluntary prayers of the night and of the day, as it is recommended to conclude with Taslīm after every two Rak‘ahs.
4. An-Nawawi said: This Hadīth is evidence that the Sunnah is to make Witr the last prayer of the night, and that its time ends with the rising of dawn. This is the famous view in our school of thought, and it is the opinion held by the majority of scholars.