Sahih Muslim Book 32, Hadith Number 6239.

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 undergo (the trouble) of running a thorn or more than that when Allah effaces his sins.