Reliance on the Book and the Sunnah - Section 3 Mishkat al-Masabih 189
Arabic hadith text
وَعَن إِبْرَاهِيم بن ميسرَة قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «مَنْ وَقَّرَ صَاحِبَ بِدْعَةٍ فَقَدْ أَعَانَ عَلَى هَدْمِ الْإِسْلَامِ» . رَوَاهُ الْبَيْهَقِيُّ فِي شُعَبِ الايمان مُرْسلا
Translation
Ibrahim b. Maisara reported God’s messenger as saying, “He who honours an innovator has assisted in undermining Islam.” Baihaqi transmitted it in mursal form in Shu'ab al-iman.