Sahih Muslim | Book 32 | Hadith Number 6258

Narrated by Nu'man b. Bashir
Nu'man b. Bashir reported Allah's Messenger (may peace be upon him) as saying: The similitude of believers in regard to mutual love, affection, fellow-feeling is that of one body; when any limb of it aches, the whole body aches, because of sleeplessness and fever.