X Research source Tahajjud is always performed in pairs of rakats and eight is seen as a good number by many Muslims. For instance, according to the Hadiths, the Prophet Muhammad frequently prayed up to thirteen rakats including Witr. However, it's possible to repeat many more if you wish. Generally, two rakats is seen as the minimum necessary for a proper Tahajjud.

Perform more rakats in pairs according to your niyyah. However, if you make a conscious decision to abandon your intention to pray Tahajjud without good reason, for example through laziness, then it may not be overlooked and a sin may be recorded. You will be rewarded as if your intention had been fulfilled. According to a hadeeth, Allah records your genuine intention to perform the Tahajjud and grants you sleep as an act of mercy. If you make an honest effort to wake up and perform the Tahajjud but accidentally sleep through the night, don't feel guilty.This is because Allah descends to the lowest heaven during the last third of the night, asking, 'Who is asking me, so I can give to him? Who is calling upon me, so I can answer him? Who is seeking my forgiveness, so I can forgive him?'' X Research source

Though the Tahajjud can be prayed at any part of the night, if possible, it is best to pray it after midnight, especially during the last third of the night. After praying the Isha prayer and before going to sleep, make arrangements to wake up during the night before the Fajr prayer (for instance, you may want to set an alarm clock or have a family member agree to wake you).

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