Tahajjud prayer

" The midnight prayer means the Tahajjud prayer. “Tahajjud” is derived from “Hujud”, meaning sleep. Tahajjud, literally, signifies giving up of sleep. The prayer was observed by the Holy Prophet (p.b.u.h.) from midnight up to the appearance of the early dawn. This prayer was specially ordained for the Holy Prophet by the following verses: “And forsake sleep by it during a part of the night, being optional for you.” “Perchance the Lord will send thee to the Praised Abode.” (17: 79Q.) The Prophet was asked to stand up in prayer at night and seek nearness to God by the following verses:
“O thou who hast wrapped thyself! Rise to pray in the night except a little or add to it, and recite it with a little or add to it, and recite the Quran well arranged. Surely the rising by night is the firmest way to tread and most impressive in speech.” (73: 1-6Q.)
According to this direction of the Almighty, the Prophet imposed upon himself the additional prayer of Tahajjud and spent the greater portion of his night in divine service. To this effect, the Quran says: “Surely the Lord knows that thou passest in prayer nearly tow-thirds of the night and (sometimes) held of it, and also a party of those who are with thee.” (73: 20Q.) These risings of the Holy Prophet (p.b.u.h.) were generally interrupted by short naps at intervals of a few minutes. In this prayer at night the Holy Prophet (p.b.u.h.) unrevealed his mind before his Great Maker with his entire self-surrender, and remained standing so long in prayer that his feet used to get swollen.
There is no fixed number of rak’ats in Tahajjud prayer. It is generally a prayer without any standard forms of rituals and verses. The great objects is to pour out one’s heart before one’s Maker most submissively and with the utmost self-surrender and self-effacement in the worshipper’s own language and preferably with the verses of the Quran which he likes most. The number of rak’ats varies form three to thirteen, including the “Witr” prayer.

(b) Excellence of night prayer
“Great rewards and merits have been promised for the night prayer. Allah descends to the lowest heaven in the latter part of the night and invites invocations and petitions. Therefore the latter part of the night, specially the middle of the latter half of the night is opportune moment for acceptance of prayers. There is a moment in the night in which the prayer of a devotee is accepted. Night prayer expiates and prevents sins. The honourable among the Muslims are those learned in the Quran and those who pray at night.”