ALLAH'S MERCY AT THE TIME OF TAHAJJUD
Rasulullah SAW said:
"At night there is such a moment in which a Muslim supplicates Allah Ta'ala for the good of this world or the Hereafter, Allah Ta'ala will grant him his request, and this moment appears every night." (Muslim)
The above Hadith bears the good fortune of acceptance of ones du'as at night. However, mention is not made of the specific moment of acceptance. Some Ulama are of the opinion that this period is not known like that of Lailatul Qadr and the special moment of acceptance on Jumu'a (Friday), while others opine that it is at midnight. (Mazahir)
In another Hadith, Rasulullah SAW said:
"The closest Allah Ta'ala gets to his servant is in the last portion of the night. If you possess the ability to be from among those who remember Allah, then become one of them." (Tirmidhi)
As for "the closeness of Allah" above, this refers to Allah's pleasure and mercy showered upon his servants who sacrifice their sleep and strive in His worship. (Mazahir)
Rasulullah SAW said:
"When one third of the night remains our Rabb, Most High, Most Exalted, descends to the first sky and announces, "Who is there to beseech Me that I may answer his prayer and who is there to seek forgiveness that I may forgive him. Then He spreads out His hands (of kindness and mercy) and proclaims, "Who will grant a loan to the One who is neither a destitute or an oppressor." (Muslim)
Explaining the above narration, Allah Ta'ala is free from bodily form and shape. He is Omnipresent and He is not confined to space. The grand scholars - Hafiz Ibn Hajar RA and Imam Malik RA have stated that "Allah Ta'ala descending to the first sky" signifies His special Mercy through which He accepts du'as and forgives sins. (Lam'aat)
As for the loan mentioned in the Hadith, this refers to bodily and financial devotions offered to Allah Ta'ala with the hope of attaining reward. (Mazahir)
THE CORRECT TIME FOR TAHAJJUD
The time of Tahajjud extends from the time of Isha' Solat until Subuh Sadiq (true dawn). Ahadith related from Aishah RA state that Nabi Muhammad SAW sometimes performed Tahajjud in the early portion of the night and on occasions when half the night had passed. However, towards the latter part of his life he frequently performed it in the last portion of the night. As the night progresses, Allah Ta'ala's Mercy and Blessings increase. Hence, the last portion of the night is most preferred.
DU'A TO ASSIST ONE IN AWAKENING FOR TAHAJJUD
A person remarked to Abdullah ibn Abbas RA: "I always intend awakening in the last portion of the night to perform Solat but sleep overpowers me."
Abdullah ibn Abbas RA replied:
"Before sleeping recite from "QUL LAW KAANAL BAHRU MIDADAL..." to the end of Surah Al-Kahf. Allah Ta'ala will waken you at whatever time you intend rising."
NUMBER OF RAKAATS IN TAHAJJUD
The number of rakaats performed by Nabi Muhammad SAW varied according to the prevailing circumstances. Although on certain occasions sufficient time was available, Nabi SAW would perform less rakaats when reciting lengthy Qiraat (i.e. when longer surahs were recited, less rakaats were performed).
Deducing from the various narrations - four to twelve rakaats in units of two or four have been recommended. However if two rakaats are performed in the prescribed time it will of course still be regarded as Tahajjud.
OCCASIONS WHEN ONE IS UNABLE TO AWAKEN FOR TAHAJJUD
Aishah RA relates:
"If for some reason Rasulullah (SAW) was unable to perform Tahajjud, he would perform twelve rakaats during the day (at the time of Dhuha - before midday)."
To continue the discussion of the above hadith, Saiyidina Umar RA relates that Rasulullah SAW said:
"Whoever was unable to complete his devotions at night should complete it in the morning before noon. It will be regarded as though he had completed it at night." (Muslim)
Nevertheless, one should not overlook it because of the time passing by, otherwise the nafs will become accustomed to omitting it.