Mujahid (may Allah have mercy on him) narrates: A man came to Sayyiduna Ibn Umar (may Allah be pleased with them both) and said: What do you say about Sayyiduna Ali (may Allah be pleased with him)? He said: "He is who he is; this is his house (his standing)." The man said: What do you say about Sayyiduna Uthman (may Allah be pleased with him)? He said: "What should I say about a man who committed a sin between himself and his Lord, and Allah forgave him, and committed a sin between you and him, and you killed him?"
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13476