Silsilat al-Ahadith al-Sahihah

It is narrated from Sayyiduna Nu’man bin Bashir (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) said: “All Muslims are like a single person. If the eye of a person is ill, the whole body feels the pain, and similarly, if there is a headache, the whole body feels the pain.”