Sahih Muslim 1375
Sahih Muslim · Book 15: The Book of Pilgrimage · Encouragement to live in Al-Madinah and to be patient on bearing its distress and hardships
Sahl b. Hunif reported that Allah's Messenger (ﷺ) pointed with his hands towards Medina and said:
وَحَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ ، حَدَّثَنَا عَلِيُّ بْنُ مُسْهِرٍ ، عَنِ الشَّيْبَانِيِّ ، عَنْ يُسَيْرِ، بْنِ عَمْرٍو عَنْ سَهْلِ بْنِ حُنَيْفٍ ، قَالَ أَهْوَى رَسُولُ اللَّهِ صلى الله عليه وسلم بِيَدِهِ إِلَى الْمَدِينَةِ فَقَالَ " إِنَّهَا حَرَمٌ آمِنٌ " .
That is a sacred territory and a place of safety.