(50) باب مَنْ نَكَثَ بَيْعَةً
Narrated Jabir:
A bedouin came to the Prophet (ﷺ) and said, "Please take my Pledge of allegiance for Islam." So the Prophet took from him the Pledge of allegiance for Islam. He came the next day with a fever and said to the Prophet (ﷺ) "Cancel my pledge." But the Prophet (ﷺ) refused and when the bedouin went away, the Prophet said, "Medina is like a pair of bellows (furnace): It expels its impurities and brightens and clears its good."
Reference: Sahih al-Bukhari 7216
In-book reference: Book 93, Hadith 76
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 9, Book 89, Hadith 323