Sahih Muslim Book 32, Hadith Number 6233.

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.

‘Aisha reported, I did not see anyone else being afflicted with more severe illness than Allah’s Messenger (may peace be upon him). In the narration transmitted by ‘Uthman there is a slight variation of wording.