Commenting on the aayah:
وَهُوَ الَّذِي جَعَلَ اللَّيْلَ وَالنَّهَارَ خِلْفَةً لِّمَنْ أَرَادَ أَن يَذَّكَّرَ أَوْ أَرَادَ شُكُورًا
«And He is the One who made the night and day to follow each other in succession, for whoever wants to be reminded of Allaah or whoever wants to give thanks for Allaah’s favors.» [Sooratul-Furqaan (25):62]
Shaykh Fawzaan (hafizahullaah) said:
So the night and the day are a tremendous bounty to be earned for a person who utilizes them in obedience to Allaah, the Mighty and Majestic. The arena for action is the night and the day. You have nothing else besides the night and the day. They are the arena for action, for good, and for pure earning for this world and the Hereafter. So, in the night and in the day, there are lessons and fawaa`id (benefits). Therefore, Allaah swore an oath by al-`Asr.