The Book of Prayers (Kitab Al-Salat)
Muslim :: Book 4 : Hadith 1591
'A'isha reported: The Messenger of Allah (may peace be upon him) used to recite in sitting position (while observing the Tahajjud prayer) and when he intended to bow, he would stand up and recite (for the duration in which) a man (ordinarily) recites forty verses.
Source materials are from the University of Southern California MSA site|
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