Sahih Muslim Book 32, Hadith Number 6258.

Chapter : There should be mutual fellow-feeling and love and the will to help each other amongst the believers.

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.