Night Prayer: As for voluntary night prayer (qiyam al-layl), it is superior to voluntary prayer during the day because it is closer to secrecy, and nearer to sincerity (Ikhlas).
Allah Most High said, “Lo! the vigil of the night is (a time) when impression is more keen and speech more certain.” [Qur’an, 73.9]
This is because the time of the night vigil (Tahajjud) is the best of times for voluntary prayer, and the closest a servant gets to his Lord. It is a time when the doors of the skies are opened, supplications answered, and needs fulfilled.
Allah Most High has praised those who wake up at night in His remembrance, supplication, seeking forgiveness, and intimate entreating (Munajat), saying, “Who forsake their beds to cry unto their Lord in fear and hope, and spend of that We have bestowed on them. No soul knows what is kept hid for them of joy, as a reward for what they used to do.”[Qur’an, 32.16-17]
And, “Or he who pays adoration in the watches of the night, prostrate and standing, bewaring of the Hereafter and hoping for the mercy of his Lord? Say: Are those who know equal with those who know not? But only those of understanding will pay heed.” [Qur’an, 39.9]
It has been said that those who worship at night will enter Paradise (without reckoning), and that standing in night prayer shortens the length of one’s Standing on the Day of Judgment.
This is why the Prophet (Allah bless him & give him peace) said, “Stick to night prayer, for it was the way of the righteous before you. Night prayer is a means of closeness to Allah Most High, of expiating for bad deeds, avoiding sins, and keeping away illness from one’s body.” Tirmidhi
*Shifa-Cure is found Qiyam al-Layl*
"You should pray Qiyam al-Layl, for it is the habit of the righteous people who came before you, and it will bring you closer to your Lord, expiate for bad deeds, prevent sin, and (expels diseases/sickness) from the body.” Tirmidhi
Difference between Qiyaam al-layl and Tahajjud
*Qiyam al-layl means: is Generally and is spending the night, or part of it, even if it is only one hour or 10 times, in prayer, reading Qur’an, remembering Allah (dhikr) and other acts of worship. It is not stipulated that it should take up most of the night.
*But Tahajjud means Specifically praying at night, and some scholars limited it to prayers that are offered at last night after sleeping also Tahajjud timing is an hour or 2 before fajr.