Sahih Muslim Book 032, Hadith Number 6234.
Hadith Section/Book: Sahih Muslim Sahih Muslim Book 32. Virtues, Good Manners and Joining Of The Ties Of Relationship
Chapter : Whenever a believer falls sick or is stricken with grief or something like it, there is a reward for him even if it is pricking of a thorn.
This hadith has been narrated on the authority of A'mash through other chains of transmitters.