"It was the noble habit of Rasulullah (Sallallaahu Alayhi Wasallam) to sleep and then wake up for tahajjud. If one is unable to wake up for tahajjud, then one may perform tahajjud before going to sleep.
It is the Sunnah of the Messenger of Allah (saws) and best if one sleeps after Isha and wakes up again to offer the Tahajjud or late night prayers, but it is not obligatory. If one finds it difficult to wake up again for Tahajjud, then there is no harm if one offers these voluntary prayers after the Isha prayers or before one goes to sleep.
May Allah Guide us all,Ameen.
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