Sunan Abi Dawud Book 5, Hadith 56
When the opening verses of Surah Al-muzammil was revealed, the Companions would pray as long as they would pray during Ramadan until its last verses were revealed. The period between the revelation of its opening and the last verses was one year.
In Surat al-Muzzammil (73), the verse: "Keep vigil at night but a little, a half thereof" (2-3) has been abrogated by the following verse: "He knoweth that ye count it not, and turneth unto you in mercy. Recite then of the Qur'an that which is easy for you" (v.20). The phrase "the vigil of the night" (nashi'at al-layl) means the early hours of the night. They (the companions) would pray (the tahajjud prayer) in the early hours of the night.
He (Ibn Abbas) says: It is advisable to offer the prayer at night (tahajjud), prescribed by Allah for you (in the early hours of the night). This is because when a person sleeps, he does not know when he will awake. The words "speech more certain" (aqwamu qilan) means that this time is more suitable for the understanding of the Qur'an. He says: The verse: "Lo, thou hast by day a chain of business" (v.7) means engagement for long periods (in the day's work).
The Messenger of Allah (ﷺ) as saying: When one you sleeps, the devil ties three knots at the back of his neck, sealing every knot with, "You have a long night, so sleep." So if one awakes and mentions Allah, a knot will be loosened; if he performs ablution another knot will be loosened; and if he prays, the third knot will be loosened; and in the morning he will be active and in good spirits; otherwise he will be in bad spirits and sluggish.