Sayyidah Fatimah bint Ali (may Allah be pleased with them both) and Sayyiduna Abdullah bin Ja'far (may Allah be pleased with him) narrate: Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) came to Sayyiduna Ammar bin Yasir (may Allah be pleased with him), and Sayyiduna Ammar (may Allah be pleased with him) was holding Sayyiduna Hasan bin Ali (may Allah be pleased with them both) by the collar. Sayyiduna Ali (may Allah be pleased with him) asked him: What is the matter between you and your nephew? Sayyiduna Ammar (may Allah be pleased with him) said: He says that Sayyiduna Uthman (may Allah be pleased with him) did not commit disbelief. Sayyiduna Ali (may Allah be pleased with him) said to him: Do you believe in something that Sayyiduna Uthman (may Allah be pleased with him) rejected, and could you reject something in which Sayyiduna Uthman (may Allah be pleased with him) believed? Sayyiduna Ammar (may Allah be pleased with him) replied: No! Sayyiduna Ali (may Allah be pleased with him) said: Then let your nephew go! When Sayyiduna Hasan (may Allah be pleased with him) had gone, Sayyiduna Ali (may Allah be pleased with him) said to Sayyiduna Ammar (may Allah be pleased with him): O Ammar! Do you not know that Sayyiduna Uthman (may Allah be pleased with him) believed in Allah Almighty and rejected al-Lat and al-Uzza? Sayyiduna Ammar (may Allah be pleased with him) replied: Yes! (i.e. I know this).
Al-Tabarani recorded it; its chain contains a narrator, al-Miswar bin al-Salt, and he is matruk (abandoned).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الفتن - أعاذنا الله منها / 12005