It is narrated from Sayyiduna Sahl bin Hunayf (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) was asked about Madinah, and he (peace and blessings be upon him) said: "It is a sanctuary, a place of safety; it is a sanctuary, a place of safety."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5591