Merits of Seeking Forgiveness in the hours before dawn
وَبِالْأَسْحَارِ هُمْ يَسْتَغْفِرُونَ (and in the hours before dawn, they used to pray for forgiveness..., 51:18) The word ashar is the plural of sahar, and it refers to the latter sixth part of the night. This verse speaks of the significance of seeking forgiveness in the latter part of the night. Another verse [ 3:17] also speaks of the significance of seeking forgiveness at the last hours of the night thus: وَالْمُسْتَغْفِرِينَ بِالْأَسْحَارِ (...and who seek forgiveness in pre-dawn hours. - 3:17) It is confirmed in the Sahih collections as well as others, from several Companions, that the Messenger of Allah ﷺ said:
"Allah, the Most High, descends each night to the lowest heaven when the last third of the night remains. He says: 'Is there anyone who is repenting, so that I may accept his repentance? Is there anyone seeking forgiveness, so that I may forgive him? Is there anyone asking of Me, so that I may grant him his request?
Here it may be noted that in this verse Allah is describing the pre-dawn prayer of forgiveness of those righteous ones who, according to the preceding verse, are preoccupied for the major part of the night with the worship of Allah and sleep very little. Thus there seems to be no link between their previous description and their description of asking for forgiveness in this verse, because forgiveness is sought when there are sins. People who spent the entire night in worshipping Allah - what does it mean to seek forgiveness of sins? The answer to this question is that these people have the true appreciation of Allah's majesty, dignity and splendour, and they realise that there are shortcomings in their night-long worship. Therefore they seek Allah's forgiveness for failing to perform His worship as due. (Mazhari)