1862 صلاة الليل والنهار مثنى مثنى
(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».

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."

صحيح - ( رواه أبو داود وأحمد والترمذي والنسائي وابن ماجه ). Sahih/Authentic. [Ibn Maajah]

هذا الحديث: أصله في الصحيحين: بلفظ:(صلاة الليل مثْنَى مثْنَى) زاد بعض الرواة: (والنَّهار) وهي زيادة ضعيفة، والمعنى: أن من أراد أن يتطوع في الليل أو النَّهار، فليُسَلِّم من كل ركعتين؛ كما جاء مُصرحا به في صحيح مسلم عن ابن عمر رضي الله عنهما لما سئل: "ما مثْنَى مثْنَى؟" قال: "أن تُسلِّم في كل ركعتين". وهذا قول أكثر العلماء في صلاة الليل أي: لا يجوز التطوع بأكثر من ركعتين في صلاة الليل، إلا ما كان من صلاة الوتر، فله الزيادة لثبوت السُّنة بذلك. أما صلاة النَّهار فلا بأس بالزيادة على ركعتين والأفضل مثْنَى مثْنَى.
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.

أن صلاة الليل والنَّهار مثْنَى مثْنَى، والصحيح الليل فقط.