12:40

You worship not besides Him except [mere] names you have named them, you and your fathers, for which Allah has sent down no authority.

12:40

مَا تَعْبُدُونَ مِن دُونِهِ إِلَّا أَسْمَاءً سَمَّيْتُمُوهَا أَنتُمْ وَآبَاؤُكُم مَّا أَنزَلَ اللَّهُ بِهَا مِن سُلْطَانٍ ۚ إِنِ الْحُكْمُ إِلَّا لِلَّهِ ۚ أَمَرَ أَلَّا تَعْبُدُوا إِلَّا إِيَّاهُ ۚ ذَٰلِكَ الدِّينُ الْقَيِّمُ وَلَٰكِنَّ أَكْثَرَ النَّاسِ لَا يَعْلَمُونَ

Sahih International

You worship not besides Him except [mere] names you have named them, you and your fathers, for which Allah has sent down no authority. Legislation is not but for Allah . He has commanded that you worship not except Him. That is the correct religion, but most of the people do not know.

Bangla

তোমরা আল্লাহকে ছেড়ে নিছক কতগুলো নামের এবাদত কর, সেগুলো তোমরা এবং তোমাদের বাপ-দাদারা সাব্যস্ত করে নিয়েছে। আল্লাহ এদের কোন প্রমাণ অবতীর্ণ করেননি। আল্লাহ ছাড়া কারও বিধান দেবার ক্ষমতা নেই। তিনি আদেশ দিয়েছেন যে, তিনি ব্যতীত অন্য কারও এবাদত করো না। এটাই সরল পথ। কিন্তু অধিকাংশ লোক তা জানে না।

 Related Ayah: 53:23

My Comments:
This aya is enough to confirm that any worship requires approval from Allah as such from his messengers for all previous nations as such from Muhammad Rasulullah Sallillahu Alaihi WaSAllam for this nation as he has instructed or showed or approved.
Traditionally this is regarded as ‘Bida’h’ according to the hadith. But logically this is just not only ‘bida’h’ but a clear shirk. Let me explain.
As Allah mentions He did not send ‘AUTHORITY’ for what they worship, therefore, it is clear that any worship needs authority from Allah. In other words, worship methods or system is Allah’s authority. Therefore, if you do not follow the ‘proper’ authority, you are giving someone else that right of ‘authority’, therefore you setting an equal to Allah by giving the authority, which belongs to Allah, to someone or something else, in this case, it is your own ‘desire’ (ideas and thoughts) as Allah mentions else where at 53:23
That’s how it becomes shirk, setting an equals to Allah, the only authority of worship. And Allah knows best.