The term 'khilafah' comes from 'khalaf', like 'rukbah' comes from 'rakab'. It is the state in which night and day succeed one another. The meaning is: He made them successors, meaning: having a succession, that this one follows that one and that one follows this one.

It is said that night and day differ, as it is said that they alternate. From this is His saying: 'And the alternation of night and day.' It is also said: 'So-and-so has a khilafah and ikhtilaf', if he frequently changes to a prominent one. And it is read: 'yudhkar' and 'yudhkar'.

And from Abu K'ab, may Allah be pleased with him: 'He remembers.' The meaning is for the observer to look at their differences, so he knows that there must be a transition from one state to another, and their change is due to a mover and changer. This is evidence of His great power, and the thankful should be grateful for the blessings in them, from the stillness at night and the activity during the day, as He, the Exalted, said: 'And of His mercy, He made for you the night and the day so that you may find rest in them and seek of His bounty.' Or they may serve as times for the remembering and the thankful; whoever misses in one of them and returns to worship can perform it in the other. And from Al-Hasan, may Allah be pleased with him:

Whoever misses his deeds of remembrance and gratitude during the day will have a chance to make up for it at night. And whoever misses at night will have a chance to make up for it during the day.