Al-Aqra', the mu'adhdhin (announcer) of Umar ibn al-Khattab said: Umar sent me to a bishop and I called him. Umar said to him: Do you find me in the Book? He said: Yes. He asked: How do you find me? He said: I find you (like a) castle. Then he raised a whip to him, saying: What do you mean by castle? He replied: An iron castle and severely trustworthy. He asked: How do you find the one who will come after me? He said: I find him a pious caliph, except that he will prefer his relatives. Umar said: May Allah have mercy on Uthman: He said it three times. He then asked: How do you find the one who will come after him? He replied: I find him like rusty iron. Umar then put his hand on his head, and said: O filthy! O filthy! He said: Commander of the Faithful! He is a pious caliph, but when he is made caliph, the sword will be unsheathed and blood will be shed. Abu Dawud said: Al-dafr means filth or evil smell.  

لَهُ عُمَرُ وَهَلْ تَجِدُنِي فِي الْكِتَابِ قَالَ نَعَمْ قَالَ كَيْفَ تَجِدُنِي قَالَ أَجِدُكَ قَرْنًا فَرَفَعَ عَلَيْهِ الدِّرَّةَ فَقَالَ قَرْنُ مَهْ فَقَالَ قَرْنٌ حَدِيدٌ أَمِينٌ شَدِيدٌ قَالَ كَيْفَ تَجِدُ الَّذِي يَجِيءُ مِنْ بَعْدِي فَقَالَ أَجِدُهُ خَلِيفَةً صَالِحًا غَيْرَ أَنَّهُ يُؤْثِرُ قَرَابَتَهُ قَالَ عُمَرُ يَرْحَمُ اللَّهُ عُثْمَانَ ثَلاَثًا فَقَالَ كَيْفَ تَجِدُ الَّذِي بَعْدَهُ قَالَ أَجِدُهُ صَدَأَ حَدِيدٍ فَوَضَعَ عُمَرُ يَدَهُ عَلَى رَأْسِهِ فَقَالَ يَا دَفْرَاهُ يَا دَفْرَاهُ فَقَالَ يَا أَمِيرَ الْمُؤْمِنِينَ إِنَّهُ خَلِيفَةٌ صَالِحٌ وَلَكِنَّهُ يُسْتَخْلَفُ حِينَ يُسْتَخْلَفُ وَالسَّيْفُ مَسْلُولٌ وَالدَّمُ مُهْرَاقٌ