(45) باب بَيْعَةِ الأَعْرَابِ
Narrated Jabir bin `Abdullah:
A bedouin gave the Pledge of allegiance to Allah's Messenger (ﷺ) for Islam and the bedouin got a fever where upon he said to the Prophet (ﷺ) "Cancel my Pledge." But the Prophet (ﷺ) refused. He came to him (again) saying, "Cancel my Pledge.' But the Prophet (ﷺ) refused. Then (the bedouin) left (Medina). Allah's Apostle said: "Medina is like a pair of bellows (furnace): It expels its impurities and brightens and clears its good."
Reference: Sahih al-Bukhari 7209
In-book reference: Book 93, Hadith 69
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 9, Book 89, Hadith 316