Arbaeen An Nawawi - Hadith 5

Aisha R.A. reported: The Messenger of Allah, peace be upon him, said:
مَنْ أَحْدَثَ فِي أَمْرِنَا هَذَا مَا لَيْسَ فِيهِ فَهُوَ رَدٌّ
Whoever innovates something into this matter of ours which does not belong to it will have it rejected.
Source: Sahih Bukhari 2550, Grade: Muttafaqun Alayhi

In another narration, the Prophet said:
مَنْ عَمِلَ عَمَلًا لَيْسَ عَلَيْهِ أَمْرُنَا فَهُوَ رَدٌّ
Whoever performs a deed that is not in accordance with our matter will have it rejected.
Source: Sahih Muslim 1718, Grade: Sahih