When reading the Quran we can obviously see that God is the supreme being , there is doubt about it , this is represented in many verses in the Quran , for example :
[ ٱللَّهُ لَآ إِلَـٰهَ إِلَّا هُوَ ٱلۡحَىُّ ٱلۡقَيُّومُۚ لَا تَأۡخُذُهُ ۥ سِنَةٌ۬ وَلَا نَوۡمٌ۬ۚ لَّهُ ۥ مَا فِى ٱلسَّمَـٰوَٲتِ وَمَا فِى ٱلۡأَرۡضِۗ مَن ذَا ٱلَّذِى يَشۡفَعُ عِندَهُ ۥۤ إِلَّا بِإِذۡنِهِۦۚ يَعۡلَمُ مَا بَيۡنَ أَيۡدِيهِمۡ وَمَا خَلۡفَهُمۡۖ وَلَا يُحِيطُونَ بِشَىۡءٍ۬ مِّنۡ عِلۡمِهِۦۤ إِلَّا بِمَا شَآءَۚ وَسِعَ كُرۡسِيُّهُ ٱلسَّمَـٰوَٲتِ وَٱلۡأَرۡضَۖ وَلَا يَـُٔودُهُ ۥ حِفۡظُهُمَاۚ وَهُوَ ٱلۡعَلِىُّ ٱلۡعَظِيمُ (٢٥٥ ]
[ Allah! there is no Allah but He―the living, the Self-subsisting, Eternal. No slumber can seize him nor sleep. His are all things in the heavens and on earth. Who is there can intercede in His presence except as He permitteth? He knoweth what (appeareth to His creatures as) Before or After or Behind them. Nor shall they compass aught of His knowledge except as He willeth. His Throne doth extend over the heavens and the earth, and He feeleth no fatigue in guarding and preserving them. For He is the Most High, the Supreme (in glory). (255) ] Sura 2 :255
[ هُوَ ٱللَّهُ ٱلَّذِى لَآ إِلَـٰهَ إِلَّا هُوَ ٱلۡمَلِكُ ٱلۡقُدُّوسُ ٱلسَّلَـٰمُ ٱلۡمُؤۡمِنُ ٱلۡمُهَيۡمِنُ ٱلۡعَزِيزُ ٱلۡجَبَّارُ ٱلۡمُتَڪَبِّرُۚ سُبۡحَـٰنَ ٱللَّهِ عَمَّا يُشۡرِڪُونَ (٢٣) هُوَ ٱللَّهُ ٱلۡخَـٰلِقُ ٱلۡبَارِئُ ٱلۡمُصَوِّرُۖ لَهُ ٱلۡأَسۡمَآءُ ٱلۡحُسۡنَىٰۚ يُسَبِّحُ لَهُ ۥ مَا فِى ٱلسَّمَـٰوَٲتِ وَٱلۡأَرۡضِۖ وَهُوَ ٱلۡعَزِيزُ ٱلۡحَكِيمُ (٢٤) ]
[ 22. Allah is He, than Whom there is no other god;- Who knows (all things) both secret and open; He, Most Gracious, Most Merciful.
23. Allah is He, than Whom there is no other god;- the Sovereign, the Holy One, the Source of Peace (and Perfection), the Guardian of Faith, the Preserver of Safety, the Exalted in Might, the Irresistible, the Supreme: Glory to Allah. (High is He) above the partners they attribute to Him.
24. He is Allah, the Creator, the Evolver, the Bestower of Forms (or Colours). To Him belong the Most Beautiful Names: whatever is in the heavens and on earth, doth declare His Praises and Glory: and He is the Exalted in Might, the Wise. ] Sura 59 : 22-24
and others .
Yet a number of christian critics of Islam tend to attack the concept of God in Islam with a certain allegation that goes like this (or close to it) :
"If the God of the Quran is supreme , why do we find him swearing by creatures and creations that are lower than him ? "
Such a claim has been put forth by many Christian apologists like my favorite missionary Rashid did in several episodes questioning Islamic monothiesm and the concept of God in Islam and Christianity , along with a youtube video he posted discussing the Quran in the Moroccan ascent and Anis Shorrosh in his debate with Shabir Ally entitled "Allah or Trinity" .
I've only seen Arabic speaking Christians put it forth , 'till this day I haven't seen an non-Arabic speaking using it in a public debate, the reason is that they understand the different meanings of the letter "waw" "و" in the Arabic language , one of these meanings is "waw al-qasam" "واو القسم" , which is used for swearing.
to answer this allegation first we look at the biblical God , and I'm surprised to find him doing the exact same thing :
[ The LORD has sworn by the Pride of Jacob : "I will never forget anything they have done. ] Amos 8:7
Therefore there is no good reason for any Christian to object against Allah (swt) swearing by a lower creation , since he swore by the pride of Jacob in the Old Testament , and pride is definitely a lower creation created by God, and God is still to supreme being in the bible , the case is closed .