Sayyiduna Bashir bin Sa'd (may Allah be pleased with him), a Companion of the Messenger of Allah (peace and blessings be upon him), said that the Messenger of Allah (peace and blessings be upon him) said: "The place of a believer in relation to a believer is the place of the head in relation to the body: whenever the body is in pain, the head feels pain for it, and whenever the head is in pain, the rest of the body feels pain."
Hadith Referenceالمعجم الكبير للطبراني / باب الباء / 1212