It is narrated from Sayyiduna Amr bin Awf bin Milhah al-Muzani (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) declared a distance of one barid (about twelve miles) in every direction around Madinah a protected area (from hunting and the like).
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14098