Described in this verse is the event of Mi` raj (the Ascent to the heavens, or al-'Isra', the midnight journey of the Holy Prophet ﷺ which is a signal honor and distinctive miracle of our Messenger of Allah ﷺ). The word: أَسْرَىٰ (asra) is a derivation from: اِسْرَىٰ (isra' ) which literally means to make someone travel at night. After that, the introduction of the word: لَيْلًا (lailan) also makes this sense very clear. Then, by placing this word as a common noun, the indication released was that during this event the time spent was that of a part of the night - not even that of the whole night.
