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.
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.