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271. Aisha narrated: “The Messenger of Allāh (peace be upon him) used to pray eleven units at night, one of which was a unit of witr. After he finished, he would lie down on his right side.” [314] Abdul Razzaq al-Badr, Some scholars extracted a gem from this hadīth: The number of units that he (peace be upon him) prayed at night was exactly the same as the units performed for the daytime obligatory prayers, which are Dhuhr, Asr and Maghrib. Ibn Hajar al-Haytamī said, This is an explicit statement to show that the least number of units for witr is one, and that a prayer of one unit is valid.
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Muhammad al-Tirmidhi (A Commentary on the Depiction of Prophet Muhammad: Shama'il Muhammadiyyah)