الفرار من الطاعون
Guidance not to enter a land where plague has broken out, and not to flee a land you are already in once it has broken out there — an early quarantine principle.
إِذَا سَمِعْتُمْ بِهِ بِأَرْضٍ فَلَا تَقْدَمُوا عَلَيْهِ، وَإِذَا وَقَعَ بِأَرْضٍ وَأَنْتُمْ بِهَا فَلَا تَخْرُجُوا فِرَارًا مِنْهُ
“If you hear of it [the plague] in a land, do not go to it; and if it breaks out in a land you are already in, do not leave fleeing from it.” (meaning, not a literal translation)
Reported during Caliph 'Umar's journey to Syria, when he turned back on hearing of an outbreak there after consulting the companions on this hadith — a real-time application of the guidance at the level of state policy, not just personal conduct.
Classical and modern commentators alike read this as an early articulation of movement restriction to contain contagion — staying put rather than either advancing into or fleeing an outbreak zone. Ibn al-Qayyim discusses both halves of the instruction as serving the same underlying goal: preventing the disease from spreading further by restricting movement in both directions, into and out of an affected area.
This two-directional restriction — don't enter an outbreak zone, don't leave one once inside — closely resembles the logic behind modern quarantine and travel-restriction public health measures, arrived at independently through epidemiological reasoning rather than this text.