The bond that Allah has set amongst the believers
Kitāb al-Muʾmin|Volume 1|Book 1|Chapter 3
92 - وعن أبي عبد الله (ع) قال المؤمنونَ في تبارّهِم وتراحمِهِم و تعاطُفِهم كمثلِ الجسدِ إذا اشتكى تداعى له سائرُه بالسّهر والحُمّى.
92. It has been reported that Abu 'Abd Allah عليه السلام said: The believers in their reverence, affection and compassion for each other are like one body; when it falls ill, it affects all over with restlessness and fever.”