Musannaf Ibn Abi Shayba 27:792

Abu Usama narrated to us, from Shu'bah, from 'Adi ibn Thabit, from 'Abdullah ibn Yazid, from Zayd ibn Thabit, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "It is Tabah (the pure/pleasant one). It expels the filth," meaning Al-Madinah.