The Time for Tahajjud

Q: Salaah-311: When does the time for Tahajjud begin?

Answer: According to the most accepted opinion, the time for Tahajjud starts after half the night has passed regardless of whether a person has slept or not (sleeping is not a precondition)3. It is however preferable for it to be performed after one has woken from one's sleep.

Fatawa Rahimiyyah vol.2