It is narrated from Sayyiduna Sahl bin Sa'd (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "The believer, among the people of faith, is like the head to the body. The believer feels pain for the people of faith just as the body feels pain for what is in the head."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5722