Short answer: Tahajjud is a voluntary night prayer performed after sleeping for a while following isha, and its time lasts until imsak.[1][2] To find the start of the last third of the night, divide the time between isha and imsak by three and subtract it from imsak: last third = imsak − (imsak − isha) / 3.
What Is Tahajjud?
The TDV Encyclopedia of Islam defines tahajjud as a voluntary prayer performed after getting up from sleep at night. What sets it apart from other voluntary prayers after isha is that it is performed after sleeping.[1] Its time lasts from waking after sleep following isha until the start of the morning time, imsak.[2]
Why The Last Third Of The Night?
In the hadith narrated by Bukhari and Muslim, the Prophet said that our Lord descends to the lowest heaven every night when the last third of the night remains and says, “Is there anyone calling upon Me, that I may answer him?” (Bukhari 1145, Muslim 758).[3] This is why the last third of the night stands out as a time for night worship. The schools of law differ on the most virtuous time for tahajjud; see the TDV Encyclopedia entry for details.[1]
The last part of the night is called seher, the time close to dawn.[4]
When Does The Night Begin?
The starting point is debated: we could not find a clear Diyanet text on whether the night should be counted from maghrib or from isha. Because tahajjud is a prayer performed after isha, AuraSleep counts the night from isha to imsak. This is a product decision; you can always choose your own time in the app.
Step By Step
As an example, take a night with isha at 20:28 and imsak at 05:47. These times are examples; take the times for your city from the Diyanet calendar or the app.
- Find the length of the night. From 20:28 to 05:47 is 9 hours 19 minutes, or 559 minutes.
- Divide by three. 559 / 3 ≈ 186 minutes, or 3 hours 6 minutes.
- Subtract from imsak. 05:47 − 3 hours 6 minutes = 02:41.
On this night the last third starts at 02:41 and lasts until imsak at 05:47. Plan tahajjud so that you finish before imsak.
The times themselves follow the Diyanet method: imsak is when the sun is 18° below the horizon and isha when it is 17° below.[5] That is why the last third moves with the seasons: it shrinks on summer nights and grows on winter nights.
Does The Moon Phase Change The Time?
No. Prayer times follow the position of the sun; the phase of the moon does not set the tahajjud time. The moon sets the Hijri calendar: Ramadan, the holy nights and the Eids.
The Tahajjud Alarm In AuraSleep
AuraSleep calculates the times on your phone, offline, and offers three options:
- Last third: The time from the formula above.
- Seher: 45 minutes before imsak.
- Custom: Any time you like.
The app only suggests; the choice is yours. Since tahajjud comes after sleep, set the alarm before you go to bed and add a backup alarm for important wake-ups.
Sources
- TDV Encyclopedia of Islam, “Teheccüd” (Turkish)
- Sorularla İslamiyet, When does the time of tahajjud begin? (Turkish)
- HadeethEnc, “Our Lord descends every night when the last third of the night remains...” (Bukhari 1145, Muslim 758)
- Sorularla İslamiyet, What is the time of seher? (Turkish)
- e-sehir, Explanation of the Diyanet imsakiye calculation, imsak 18° and isha 17° (Turkish)