Whoever introduces into this matter of ours (Islam) something that does not belong to it shall have it rejected

Acts of worship are based on what is prescribed in the Qur’an and Sunnah. We worship Allah Almighty only in accordance with what He has prescribed and not in accordance with religious innovations and heresies.
Religion is not based on reason or juristic discretion; rather, it is based on following the Messenger of Allah (may Allah's peace and blessings be upon him).
This Hadīth is proof of the perfection of the religion.
"Bid‘ah" (religious innovation): It is every belief, saying, or act that is newly introduced in the religion, which neither existed during the time of the Prophet (may Allah's peace and blessings be upon him) nor during the time of his Companions.
This Hadīth represents one of the fundamentals of Islam. It acts as a criterion for deeds. Every deed that is not exclusively devoted to Allah Almighty, its doer will not be rewarded for it and the same rule applies to every deed that does not conform with the Prophet's Sunnah will be rejected upon its doer.
The prohibited innovations are those related to religion and not those related to worldly affairs.