Hadith: (Voluntary) prayer in both the day and night is performed two by two

عن ابن عمر رضي الله عنهما ، عن النبي صلى الله عليه وسلم قال: «صلاة الليل والنَّهار مثْنَى مثْنَى».
[صحيح] - [رواه أبو داود وأحمد والترمذي والنسائي وابن ماجه]

Ibn ‘Umar (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "(Voluntary) prayer in both the day and night is performed two by two."
[Authentic hadith] - [Narrated by Ibn Majah - Narrated by At-Termedhy - An-Nasaa’i - Narrated by Abu Daoud - Narrated by Ahmad]

Explanation

Explanation of the Hadīth: "(Voluntary) prayer in both the day and night is performed two by two." The origin of this Hadīth was narrated by Al-Bukhāri and Muslim with the wording: "The night prayer is to be performed in two by two." Some narrators added "and the day prayer", but this addition is weak. The meaning is that anyone wishes to perform voluntary prayers at night or in the daytime, he should make Taslīm after each two Rak‘ahs. This was explicitly stated in Sahīh Muslim in the Hadīth reported by Ibn ‘Umar (may Allah be pleased with him). When Ibn ‘Umar was asked about the meaning of "two by two", he said: "That you make Taslīm after each two Rak‘ahs." This is the opinion of the majority of scholars concerning the night prayer. In other words, it is not permissible to offer voluntary prayers at night with more than two Rak‘ahs per each prayer. Witr prayer is an exception to this ruling, and the person can perform more than two Rak‘ahs in it, because this is established by the Sunnah. In the voluntary prayers during the daytime, it is permissible for the Muslim to perform more than two Rak‘ahs per each prayer. However, it is preferable to perform them two by two as well.