The Book of the Believer · Hadith 90 (#Ḥadīth #7)
Chapter 3 | The bond that Allah has set amongst the believers
90 - وعن أبي عبد الله (ع) قال لا والله، لا يكونُ المؤمن مؤمناً أبداً حتىّ يكونَ لأخيه مثل الجسدِ إذا ضرب عليه عرقٌ واحد تداعت له سائرُ عروقه.
90. It has been reported that Abu 'Abd Allah said: Nay, by Allah! A believer is not a true believer ever until he acts as the body of his brother; when one vein in it is struck, it evokes the rest of the body.
Gradings are classical jarḥ-wa-taʿdīl, name-matched to a rijāl index (not individually re-verified).