Sa'id bin al-Musayyib narrates: Sayyiduna Uthman (may Allah be pleased with him) had a particular doorkeeper who used to go out ahead of him to the prayer. One day he went out to pray, with the doorkeeper ahead of him. Then he came back, and the doorkeeper sat down in a corner. He folded his cloak, placed it under his head and lay down, and placed his whip in front of him. Meanwhile Sayyiduna Ali (may Allah be pleased with him) came, wearing a lower garment and an upper cloak, with a staff in his hand. When the doorkeeper saw him from afar, he said: "There is Sayyiduna Ali (may Allah be pleased with him) coming." Sayyiduna Uthman (may Allah be pleased with him) sat up and wrapped his cloak around himself. Then Sayyiduna Ali (may Allah be pleased with him) came and stood at his head and said: "Have you bought the land of the family of so-and-so, when the endowment of the Messenger of Allah has a right in its water? I know that no one but you could buy it." Sayyiduna Uthman (may Allah be pleased with him) stood up, and words passed between the two of them that I will not narrate until I appear before Allah Almighty. Meanwhile Sayyiduna al-Abbas (may Allah be pleased with him) came and intervened between them. Sayyiduna Uthman (may Allah be pleased with him) had raised the whip against Sayyiduna Ali (may Allah be pleased with him), and Sayyiduna Ali (may Allah be pleased with him) had raised the staff against Sayyiduna Uthman (may Allah be pleased with him). Sayyiduna al-Abbas (may Allah be pleased with him) kept trying to calm them both, saying to Sayyiduna Ali (may Allah be pleased with him): "He is the Commander of the Believers," and saying to Sayyiduna Uthman (may Allah be pleased with him): "He is your cousin." He kept doing so until both of them fell silent. (The narrator says:) The next day I saw the two of them, each holding the other's hand, and they were talking with each other.
Al-Tabarani recorded it in al-Mu'jam al-Awsat; the chain of this report contains a group of narrators whom I do not know.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الفتن - أعاذنا الله منها / 11994