Umar on Nifaq: I fear knowledgeable hypocrites in the Ummah

Abu Uthman al-Hindi reported: Umar ibn al-Khattab, may Allah be pleased with him, said, “Verily, what I fear most for this nation is a learned hypocrite.” It was said, “How is he a learned hypocrite?” Umar said, “He is learned with his tongue, but he is ignorant of the heart and good deeds.”

Source: al-Aḥādīth al-Mukhtārah 236

عَنْ أَبِي عُثْمَانَ النَّهْدِيِّ قَالَ قَالَ عُمَرَ بْنَ الْخَطَّابِ رضي الله عنه إِنَّ أَخْوَفَ مَا أَخَافُ عَلَى هَذِهِ الْأُمَّةِ الْمُنَافِقُ الْعَلِيمُ قِيلَ وَكَيْفَ يَكُونُ الْمُنَافِقُ الْعَلِيمُ قَالَ عَالِمُ اللِّسَانِ جَاهِلُ الْقَلْبِ وَالْعَمَلِ

236 الأحاديث المختارة