ذِكْرُ الزَّجْرِ عَنْ قَوْلِ الْمَرْءِ بِالْعَدْوَى، وَالصَّفَرِ الَّذِي كَانَ يَقُولُ بِهِ أَهْلُ الْجَاهِلِيَّةِ
There is no infection, no safar, no hama. A desert Arab said: Messenger of Allah, how is it that when the camel is in the sand it is like a deer-then a camel afflicted with scab mixes with it and it is affected by sub? He (the Holy Prophet) said: Who infected the first one? Note: The majority of scholars interpret this to mean that these things in and of themselves do not transmit or cause harm through supernatural or hidden means but that Allah is ultimately in control and any fearful superstition around these is false. (Using translation from Muslim 2220a)
قَالَ رَسُولُ اللَّهِ ﷺ «لَا عَدْوَى وَلَا صَفَرَ وَلَا هَامَةَ» فَقَالَ الْأَعْرَابِيُّ يَا رَسُولَ اللَّهِ فَمَا بَالُ الْإِبِلِ تَكُونُ فِي الرَّمْلِ كَأَنَّهَا الظِّبَاءُ فَيَجِيءُ الْبَعِيرُ الْأَجْرَبُ فَيَدْخُلُ فِيهَا فَيُجْرِبُهَا؟ قَالَ «فَمَنْ أَعْدَى الْأَوَّلَ؟ »