Sahih Muslim Book 32, Hadith Number 6238.

Chapter : Whenever a believer falls sick or is stricken with grief or something tike it, there is a reward for him even if it is pricking of a thorn.

‘Aisha reported Allah’s Messenger (may peace be upon him) as saying: A believer does not receive (the trouble) of running a thorn or more than that but Allah elevates him in rank or effaces his sins because of that.