Messenger of Allah ﷺ said, 'There is no 'Adwa (no disease is conveyed from the sick to the healthy without Allah's permission), nor Safar, nor Hama." A bedouin stood up and said, "Then what about my camels? They are like deer on the sand, but when a mangy camel comes and mixes with them, they all get infected with mangy." The Prophet ﷺ said, "Then who conveyed the (mange) disease to the first one?"  

إِنَّ رَسُولَ اللَّهِ ﷺ قَالَ لاَ عَدْوَى وَلاَ صَفَرَ وَلاَ هَامَةَ فَقَالَ أَعْرَابِيٌّ يَا رَسُولَ اللَّهِ فَمَا بَالُ إِبِلِي تَكُونُ فِي الرَّمْلِ كَأَنَّهَا الظِّبَاءُ فَيَأْتِي الْبَعِيرُ الأَجْرَبُ فَيَدْخُلُ بَيْنَهَا فَيُجْرِبُهَا فَقَالَ فَمَنْ أَعْدَى الأَوَّلَ رَوَاهُ الزُّهْرِيُّ عَنْ أَبِي سَلَمَةَ وَسِنَانِ بْنِ أَبِي سِنَانٍ