Fiqh-us-Sunnah Volume 3, Zakaat and Fasting, Fiqh 3.145.
Section : Night of Qadr, it is preferred to seek this night.
It is preferred to seek this night during the last ten nights of Ramadan, as the Prophet, upon whom be peace, strove his best in seeking it during that time. We have already mentioned that the Prophet would stay up during the last ten nights, would wake his wives, and then would remain apart from them to worship.