Sahih Muslim Book 32, Hadith Number 6236.

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.

This hadith has been transmitted on the authority of jarir and the hadith transmitted on the authority of Abu Mu’awiya there is an addition of these words: He said: Yes, by Him in Whose Hand is my life, there is no Muslim upon the earth.” The rest of the hadith is the same.