Asim (may Allah have mercy on him) said that Sayyiduna Anas bin Malik (may Allah be pleased with him) was asked: Did the Messenger of Allah (peace and blessings be upon him) make Madinah sacred? He said: "Yes, it is sacred; Allah and His Messenger (peace and blessings be upon him) made it sacred. Its fresh grass is not to be cut. Whoever does that, upon him is the curse of Allah, the angels and all the people."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9960