Hadith 2:65
Ziyad b. Hudair said that ‘Umar asked him whether he knew what demolishes Islam, and that when he replied that he did not, he said, "The slip of a learned man, the disputation of a hypocrite about the Book, and the rule of imams who lead men astray.” Darimi transmitted it.
وَعَن زِيَاد بن حدير قَالَ: قَالَ لِي عُمَرُ: هَلْ تَعْرِفُ مَا يَهْدِمُ الْإِسْلَامَ؟ قَالَ: قُلْتُ: لَا. قَالَ: يَهْدِمُهُ زَلَّةُ الْعَالِمِ وَجِدَالُ الْمُنَافِقِ بِالْكِتَابِ وَحُكْمُ الْأَئِمَّةِ المضلين ". رَوَاهُ الدِّرَامِي
Original Reference: Mishkat al-Masabih 269