وَبِالْأَسْحَارِ هُمْ يَسْتَغْفِرُونَ
And in the early part of the morning they asked forgiveness.
(Sūratuz Zāriyāt, No. 51, Āyat 18)
One of the qualities of the true believers as described in the verse above is seeking forgiveness in the very early hours of the morning. This refers to the Salātul Layl, the prayer recited after midnight and before Fajr time, for the qunūt in this salāt is an entreaty for forgiveness. The word sahr means covering or concealed, and since at that time of the night all things are covered with a darkness and silence, it is referred to as the time of sahr. The Holy Prophet (s) is reported to have said about this verse: I prefer the last part of the night for Tahajjud (Salātul Layl) rather than the first part because Allah has said and in the early part of the morning they seek forgiveness (quoted in Tafsīr Namuneh). He has also said that the virtuous people who will inherit Paradise seek forgiveness from God seventy times at the time of sahr.
One of the qualities of the true believers is supplicating to God in the very early hours of the morning. When all others are asleep, or perhaps involved in frivolous activities, the believer turns to the Lord and opens up his heart to Him. He seeks forgiveness, knowing that at this opportune hour, Allah responds with much mercy and grace. In a beautiful Du‘ā recommended by Imam al-Sajjād (a) for recitation before beginning Salātul Layl, we say: My God, the stars of Your sky have descended and the eyes of Your people are sleeping and the voices of Your servants and Your animals have become silent, and the kings have locked their doors and its guards are moving around it, and they are guarded from he who wishes to ask them for a need or to get a benefit from them. But You my God, are Ever Living, Subsistent, slumber or sleep does not overtake you (Tahjjud Salāt, pp. 25 – 26)
During the day many things occupy the time and mind of the human being. It is difficult to have peace of mind and heart so necessary for good worship. But at night when the demands of the material world are quiet for a while the human being acquires a special state of mind and energy which is very conducive to increasing spirituality and strengthening his connection with his Creator. That is why the friends of Allah and those who seek nearness to Him always make the most of the last part of the night. They purify their souls, enliven their hearts, strengthen their will, and perfect their sincerity, through worship at this special time.
The month of Ramadan is the best time to form the habit of Salātul Layl. Even though the nights are short, when we wake up for suhūr, a little time must be set aside for this Night Prayer. If not the entire 11 Rakā‘ats of prayers, then at least the last three rakā‘āt should be recited. It is an excellent habit to form, one that will last into the rest of the months. As Imam Sajjad (a) says in the Du‘ā to welcome the holy month of Ramadan: O God, make us like this in the other months and days as long as You give us life (Sahīfa, 44:18).
Sources: Imam ‘Ali Zaynul ‘Ābidin, Sahifa Sajjādiyya; Āyatullāh Nāsir Makārim Shirāzī (ed.), Tafsīr-e Namūne; Academy for Learning Islam, Tahajjud Salāt