Please explain to me how to pray Tahajjud Salat including all information about it, including the times to start it and how long you pray it. If you have to pray it for hours, how can this be done if you have not memorized long Surahs'?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

There is no difference between Tahajjud and Qiyam al-layl (standing in prayer by night). If the prayer is performed after one had slept then it is called Tahajjud otherwise it is called Qiyam-al-layl.

There is much evidence in Quran and the Sunnah proving the excellence and merits of Tahajjud.

Allah Says (what means): {Is one who is obedient to Allah, prostrating himself or standing (in prayer) during the hours of the night, fearing the Hereafter and hoping for the Mercy of his Lord (like one who disbelieves)? Say: "Are those who know equal to those who know not?" It is only men of understanding who will remember (i.e. get a lesson from Allah's Signs and Verses).}[Quran 39:9]. Also, Allah praised those who perform the late night prayers; Allah Says (what means): {Their sides forsake their beds, to invoke their Lord in fear and hope, and they spend (in charity in Allah's Cause) out of what We have bestowed on them. No person knows what is kept hidden for them of joy as a reward for what they used to do.} [Quran 32:16-17]

‘Abdullah Ibn Salaam said: "When the Prophet came to Madeenah, the people gathered around him and I was one of them. I looked at his face and understood that it was not the face of a liar. The first words I heard him saying were: “O people, spread the Salaam, feed the people, keep the ties of kinship, and pray during the night while the others are sleeping and you will enter Paradise in peace.” [Al-Hakim, Ibn Majah, At-Tirmithi]

Moreover, the Prophet said: ''The best prayer after the obligatory prayer is the prayer which is performed in the last part of the night". [Muslim]

Therefore, the night prayer is a confirmed Sunnah, its rule does not change even in the month of Ramadan. However, performing it during Ramadan is better than during other months.

The time of Tahajjud (Qiyam al-layl) starts after the obligatory prayer of ‘Isha’ and extends until Fajr. There is no specific time for this prayer so it may be performed at any time of the night but the preferred time is the last third of the night.

Besides, there is no specific number of Rak’ahs for this night prayer but the Prophet never prayed more than thirteen Rak’ahs during Ramadan or at any other time.

The Sunnah is to pray the night prayer in sets of two Rak’ahs. It is recommended to shorten the first two Rak’ahs making the remaining Rak’ahs longer. And then one should end it with one Rak’ah of Witr. One may also say the Qunoot supplication in the Witr prayer if he likes.

Finally, it should be mentioned that the person who does not memorize much Quran may recite many short Chapters in one Rak’ah or he may recite while looking at the Mushaf (the Arabic text of the Quran).

Allah knows best.