Surah Al Furqan Tafseer

وَهُوَ الَّذِي جَعَلَ اللَّيْلَ وَالنَّهَارَ خِلْفَةً

And He it is Who has put the night and the day in succession (Khilfatan),

meaning, each one comes after the other, in a never-ending alternation. When one goes the other comes, and vice versa, as Allah says:

وَسَخَّر لَكُمُ الشَّمْسَ وَالْقَمَرَ دَايِبَينَ

And He has made the sun and the moon, both constantly pursuing their courses. (14:33)

يُغْشِى الَّيْلَ النَّهَارَ يَطْلُبُهُ حَثِيثًا

He brings the night as a cover over the day, seeking it rapidly. (7:54)

لَا الشَّمْسُ يَنبَغِى لَهَأ أَن تدْرِكَ القَمَرَ

It is not for the sun to overtake the moon. (36:40)

لِّمَنْ أَرَادَ أَن يَذَّكَّرَ أَوْ أَرَادَ شُكُورًا

for such who desires to remember or desires to show his gratitude.

means, He has caused them both to follow one another to show the times when His servants should worship Him. So whoever misses an act of worship during the night can make it up during the day, and whoever misses an act of worship during the day can make it up during the night.

It was recorded in a Sahih Hadith:

إِنَّ اللهَ عَزَّ وَجَلَّ يَبْسُطُ يَدَهُ بِاللَّيْلِ لِيَتُوبَ مُسِيءُ النَّهَارِ وَيَبْسُطُ يَدَهُ بِالنَّهَارِ لِيَتُوبَ مُسِيءُ اللَّيْل

Allah spreads forth His Hand at night for the one who has done evil during the day to repent, and He spreads forth His Hand during the day for the one who has done evil during the night to repent.

Mujahid and Qatadah said:

"Khilfatan means different, i.e., because one is dark and the other is light.