This hadeeth comes under the following 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
'A'isha reported: I heard Allaah's Messenger (sallAllaahu alayhi wa sallam) as saying: There is nothing (in the form of trouble) that comes to a believer even if it is the pricking of a thorn that there is decreed for him by Allaah good or his sins are obliterated.