Narrated `Asim:I said to Anas, "Did Allah's Messenger (ﷺ) make Medina a sanctuary?" He replied, "Yes, (Medina is a sanctuary from such-and-such place to such-and-such place. It is forbidden to cut its trees, and whoever innovates an heresy in it or commits a sin therein, will incur the curse of Allah, the angels, and all the people." Then Musa bin Anas told me that Anas added, "..... or gives refuge to such an heretic or a sinner..."
حَدَّثَنَا مُوسَى بْنُ إِسْمَاعِيلَ، حَدَّثَنَا عَبْدُ الْوَاحِدِ، حَدَّثَنَا عَاصِمٌ، قَالَ قُلْتُ لأَنَسٍ أَحَرَّمَ رَسُولُ اللَّهِ صلى الله عليه وسلم الْمَدِينَةَ. قَالَ نَعَمْ مَا بَيْنَ كَذَا إِلَى كَذَا، لاَ يُقْطَعُ شَجَرُهَا، مَنْ أَحْدَثَ فِيهَا حَدَثًا فَعَلَيْهِ لَعْنَةُ اللَّهِ وَالْمَلاَئِكَةِ وَالنَّاسِ أَجْمَعِينَ. قَالَ عَاصِمٌ فَأَخْبَرَنِي مُوسَى بْنُ أَنَسٍ أَنَّهُ قَالَ أَوْ آوَى مُحْدِثًا.
Bukhari
Holding Fast to the Qur'an and Sunnah • Hadith 37