Night of 27th Rajab.
extract from: http://www.angelfire.com/ak5/thanvislam1400/night_of_27th_rajab.htm
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The month of Rajab, which is the seventh month of the Islamic lunar calendar, is a blessed month as a whole. It was regarded as one of the four sacred months (al-Ashhur al-Hurum) in which battles were prohibited in the time of the Messenger of Allah (Allah bless him & give him peace).