ENOfficial
‘A’isha reported God’s messenger as saying, “If anyone introduces into this affair of ours anything which does not belong to it, it is rejected.” (Bukhari and Muslim.)
Source: sunnah.com
Other translations
Arabic
عَنْ عَائِشَةَ قَالَتْ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «مَنْ أَحْدَثَ فِي أَمْرِنَا هَذَا مَا لَيْسَ مِنْهُ فَهُوَ رد»
sunnah.com