Allah T'ala says in the Holy Quran:

إِنَّ رَبَّكُمُ اللّهُ الَّذِي خَلَقَ السَّمَاوَاتِ وَالأَرْضَ فِي سِتَّةِ أَيَّامٍ ثُمَّ اسْتَوَى عَلَى الْعَرْشِ يُغْشِي اللَّيْلَ النَّهَارَ يَطْلُبُهُ حَثِيثًا وَالشَّمْسَ وَالْقَمَرَ وَالنُّجُومَ مُسَخَّرَاتٍ بِأَمْرِهِ أَلاَ لَهُ الْخَلْقُ وَالأَمْرُ تَبَارَكَ اللّهُ رَبُّ الْعَالَمِينَ

(7:54) Surely your Lord is none other than Allah, Who created the heavens and the earth in six days, and then ascended His Throne; Who causes the night to cover the day and the day swiftly pursues the night; Who created the sun and the moon and the stars making them all subservient to His command. Lo! His is the creation and His is the command. Blessed is Allah,  the Lord of the universe.

The word 'day' in the above verse has been used either in the usual sense of the twenty-four hour unit of time, or in a more general sense of 'period' of time such as in the following verses of the Qur'an:

وَيَسْتَعْجِلُونَكَ بِالْعَذَابِ وَلَن يُخْلِفَ اللَّهُ وَعْدَهُ وَإِنَّ يَوْمًا عِندَ رَبِّكَ كَأَلْفِ سَنَةٍ مِّمَّا تَعُدُّونَ


Verily a Day in the sight of your Lord is like a thousand years of your reckoning (al-Hajj 22: 47).

تَعْرُجُ الْمَلَائِكَةُ وَالرُّوحُ إِلَيْهِ فِي يَوْمٍ كَانَ مِقْدَارُهُ خَمْسِينَ أَلْفَ سَنَةٍ 


The angels and the Spirit ascend unto Him on a Day the measure of which is fifty thousand years (al-Ma'arij 70: 4).

It is very difficult to appreciate fully the exact nature of the Qur'anic statement: '(Allah) ascended the Throne.' One possibility is that after the creation of the universe, God focused His effulgence at a particular point in His Kingdom which is known as the Throne, from where He showers the blessings of life and power, and governs the whole universe.
It is possible that the word 'Throne' stands for dominion and authority and that God's ascending the Throne signifies His actual taking over the reins of the universe after having created it. Whatever the exact meaning of the expression '(Allah) ascended the Throne', the main thrust of the verse is that God is not just the creator of the universe, but is also its sovereign and ruler; that after creating the universe He did not detach Himself from, nor became indifferent to, His creation. On the contrary, He effectively rules over the universe as a whole as well as every part of it. All power and sovereignty rest with Him. Everything in the universe is fully in His grip and is subservient to His will. Every atom is bound in obedience to Him. The fate of everything existent is in His Hands. Thus the Qur'an undermines the very basis of the misconception which leads man at times to polytheism, and at others to self-glorification and so to rebellion against God. This is the natural corollary of considering God divorced from the affairs of the universe. In such cases, there are two possibilities. One, that beings other than God are considered to have the power to make or mar man's destiny. Here, man is bound to turn to those beings in devotion and subservience. The second possibility is for man to consider himself as the master of his own destiny. Here, man considers himself independent of, and indifferent to, any higher being.

It is significant that the words and figures of speech employed by the Qur'an to denote the relationship between God and man are closely related to kingship, dominion, and sovereignty. This is too conspicuous a fact to be missed by any careful student of the Qur'an. It is strange, however, that it has led some superficial critics and persons of biased outlook to conclude that the Qur'an reflects the milieu in which man's outlook was dominated by monarchical concepts, and that therefore its 'author', who in their view was the Prophet Muhammad (peace be on him), presented God as a sovereign ruler, an absolute monarch.
Quite contrary to this is the fundamental truth which the Qur'an emphatically affirms - God's sovereignty over the heavens and the earth. It negates, with equal emphasis, that sovereignty belongs to anyone else. Such a doctrine demolishes the very assumption on the basis of which the above erroneous conclusion was derived. The Qur'anic concept of God's sovereignty is in sharp contrast to the idea that creatures of God may lay claim to sovereignty and kingship. In contrast to the weak, mortal kings of the world, God is eternal and all-powerfuL This undermines the very basis of the misconceived criticism that Islam has a monarchical basis since no human being can conform to the Islamic description of the sovereign. All sovereignty vests in the One True God. Hence, all those who claim total or partial sovereignty either for any person or group of people are merely cherishing an illusion. It is evident, therefore, that it is totally inappropriate for man, who is a part of the universe created and governed by God, to adopt any other attitude than that of acknowledging God as the only object of worship and as the only sovereign in a societal and political sense. (Tafheemul Quran)