One of the clear commandments in the Quran is to never associate any partners with God.
[4:36] You shall worship GOD alone—do not associate anything with Him…
وَاعْبُدُوا اللَّهَ وَلَا تُشْرِكُوا بِهِ شَيْئًا
Sadly such a simple commandment is at odds with most people who self identify as Muslims. Proof of this is that in almost every masjid in the world a person cannot enter without seeing the prophets name propped up right next to the name of God.
God informs us that the places of worship belong to God alone and not to call on the name of anyone else next to the name of God.
[72:18] The places of worship belong to GOD; do not call on anyone else beside GOD.
وَأَنَّ الْمَسَاجِدَ لِلَّهِ فَلَا تَدْعُوا مَعَ اللَّهِ أَحَدًا
It doesn’t matter if a masjid has 99 names of God and a single mention of Muhammad next to the name of God, this is still idol worship and prohibited. A true believer of God should be 100% satisfied with mentioning only the name of God at every place of worship and in their declaration of faith (Shahadah).
The declaration of faith in the Quran is mentioned 19 times, and it always only mentions God alone. In Sura 47, entitled Muhammad we see the Shahadah clearly stated for us.
[47:19] You shall know that: “There is no other god beside GOD,” and ask forgiveness of your sins and the sins of all believing men and women. GOD is fully aware of your decisions and your ultimate destiny.
فَاعْلَمْ أَنَّهُ لَا إِلَٰهَ إِلَّا اللَّهُ وَاسْتَغْفِرْ لِذَنْبِكَ وَلِلْمُؤْمِنِينَ وَالْمُؤْمِنَاتِ وَاللَّهُ يَعْلَمُ مُتَقَلَّبَكُمْ وَمَثْوَاكُمْ
God even confirms that this is the Shahadah of God, the angels, and the knowledgable.
[3:18] GOD bears witness that there is no god except He, and so do the angels and those who possess knowledge. Truthfully and equitably, He is the absolute god; there is no god but He, the Almighty, Most Wise.
شَهِدَ اللَّهُ أَنَّهُ لَا إِلَٰهَ إِلَّا هُوَ وَالْمَلَائِكَةُ وَأُولُو الْعِلْمِ قَائِمًا بِالْقِسْطِ لَا إِلَٰهَ إِلَّا هُوَ الْعَزِيزُ الْحَكِيمُ
Yet most Muslims still insist on including the name of the prophet next to the name of God in their Shahadah. This goes in direct conflict with what God tells us in the Quran. Ironically, the only time we see individuals bear witness to Muhammad being a messenger of God in the Quran is by the hypocrites in Sura 63 which appropriately enough is entitled The Hypocrites (Al-Munaafeqoon). In this verse God calls such people who do this not just hypocrites, but also liars.
[63:1] When the hypocrites come to you they say, “We bear witness that you are the messenger of GOD.” GOD knows that you are His messenger, and GOD bears witness that the hypocrites are liars.
The reason the hypocrites are liars is because unless they were present when prophet Muhammad was summoned to the High Horizon where he received the revelation of the Quran in his heart then they cannot claim to bear witness. God confirms this in the following verses:
[28:44] You were not present on the slope of the western mount, when we issued the command to Moses; you were not a witness.
وَمَا كُنْتَ بِجَانِبِ الْغَرْبِيِّ إِذْ قَضَيْنَا إِلَىٰ مُوسَى الْأَمْرَ وَمَا كُنْتَ مِنَ الشَّاهِدِينَ
Then why is it that with such clear commandments from God and simple logic that most people still fail to take heed? The answer is because most people who claim to believe do not do so without committing idol worship.
[12:106] The majority of those who believe in GOD do not do so without committing idol worship.
وَمَا يُؤْمِنُ أَكْثَرُهُمْ بِاللَّهِ إِلَّا وَهُمْ مُشْرِكُونَ
In order to determine if a person is a true worshiper of God alone or an idol worshiper, God provides us the following simple test: if someone is only satisfied when another entity is mentioned beside God, then they are not a worshiper of God alone.
[39:45] When GOD ALONE is mentioned, the hearts of those who do not believe in the Hereafter shrink with aversion. But when others are mentioned beside Him, they become satisfied.
وَإِذَا ذُكِرَ اللَّهُ وَحْدَهُ اشْمَأَزَّتْ قُلُوبُ الَّذِينَ لَا يُؤْمِنُونَ بِالْآخِرَةِ وَإِذَا ذُكِرَ الَّذِينَ مِنْ دُونِهِ إِذَا هُمْ يَسْتَبْشِرُونَ