Sayyiduna Ibn Umar (may Allah be pleased with them both) said: A man asked the Messenger of Allah (peace and blessings be upon him) about the night prayer, so he (peace be upon him) said: "It is two by two rak‘ahs, then when one fears that morning is near, he should pray one rak‘ah, and that will make what he has prayed odd (witr)." Imam Darimi (may Allah have mercy on him) was asked: Do you also say this? He said: Yes. (That is, praying one rak‘ah of witr is correct.)
Hadith Referenceسنن دارمي / من كتاب الصللاة / 1623
Hadith Gradingتحقیق (حسین سلیم أسد الدارانی):إسناده جيد ولكن الحديث متفق عليه، [مكتبه الشامله نمبر: 1625]
Hadith Takhrijاس روایت کی سند جید اور یہ حدیث متفق علیہ ہے۔ اور (1498) نمبر پر گذر چکی ہے۔
Brief Explanation
(Commentary on Ahadith 1621 to 1623)
That is, one should pray in sets of two rak‘ahs (units of prayer) as many rak‘ahs as one wishes. The Messenger of Allah (sallallahu alayhi wa sallam) did not specify a limit as to how many rak‘ahs should be prayed. However, the Messenger of Allah (sallallahu alayhi wa sallam) performed at most thirteen rak‘ahs, as has already been mentioned in the hadith of Sayyidah A’ishah (radi Allahu anha). Therefore, if one suffices with this, it is in complete accordance with the Sunnah of the Messenger (sallallahu alayhi wa sallam). And most often, he (sallallahu alayhi wa sallam) would pray eleven rak‘ahs, as is also mentioned in the following hadith.