Jami` at-Tirmidhi 3920
جامع الترمذي#3920SahihNarrated Jabir:that a Bedouin gave the pledge to the Messenger of Allah (ﷺ) for Islam, then he was afflicted by the sickness in Al-Madinah. So the Bedouin went to the Messenger of Allah (ﷺ) and said: "Take back my pledge." But the Messenger of Allah (ﷺ) refused. Then the Bedouin left and came back and said: "Take back my pledge," and he refused. Then the Messenger of Allah (ﷺ) said: "Al-Madinah is but like bellows, it expels its filth and purifies its good
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirSahih
Al-AlbaniSahih
Bashar Awad MaaroufHasan Sahih
Zubair Ali ZaiSahih - Agreed Upon
In-book reference: 49:320