Sayyiduna Abu Musa al-Ash'ari (may Allah be pleased with him) narrates that he heard the Prophet (peace and blessings be upon him) say: "You will not be believers until you show mercy to one another." The people said: "O Messenger of Allah, all of us are merciful." The Prophet (peace and blessings be upon him) said: "What is meant is not that one of you shows mercy to his companions; rather, what is meant is mercy to people, mercy to all (or in general)."
Al-Tabarani recorded it, and its narrators are the narrators of the Sahih.