Sahih Muslim
The Book of Virtue, Good Manners and Joining of the Ties of Relationship (Kitab Al-Birr was-Salat-I-wal-Adab)
Book Number: 032 / Hadith Number: 6240
'A'isha said: No trouble comes to a believer even if it is the pricking of a thorn that it becomes (the means) whereby his sins are effaced or his sins are obliterated. Yazid says: He does not know which word 'Urwa said (whether he said Qussa or Kuffira).