لا يورد ممرض على مصح
Guidance not to bring a sick animal near a healthy herd, given alongside the theological point that disease does not spread except by Allah's permission.
لَا يُورِدَنَّ مُمْرِضٌ عَلَى مُصِحٍّ
“The owner of diseased [camels] should not bring them to graze among healthy ones.” (meaning, not a literal translation)
Given in the same discussion as 'There is no 'adha [contagion occurring independently of Allah's decree]' — scholars read the two together as affirming both divine causation and the wisdom of ordinary precaution, the same reconciliation pattern seen in the leprosy-avoidance entry.
Ibn al-Qayyim treats this as consistent, not contradictory, with hadith negating independent contagion: precaution is itself part of how Allah's decree ordinarily operates. He extends the underlying logic here to human illness as well, treating livestock separation as one clear, concrete example of a broader precautionary principle running through several entries on this site.
Modern veterinary biosecurity practice is built substantially around exactly this principle — isolating sick animals from healthy herds to prevent disease spread — arrived at through germ theory and epidemiology rather than this text, but reaching the same practical conclusion.