Authentic
graded by Al-Albani
Mishkat al-Masabih 269
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
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.
Reported by Ad-Darimi (No. 216). Cited in Mishkat al-Masabih (No. 269).