Were Ali ibn Abi Talib and Uthman, may Allah be pleased with them, killed by Muslims? What were the reasons for the discord (fitna) among the Companions during that period, and what books have addressed this topic?

The companions of Muhammad, peace and blessings be upon him, are the best companions for the best prophet, especially the Rightly Guided Caliphs. Allah has praised them in the Quran. One must refrain from delving into the disputes and conflicts that occurred between them, while believing that they are the best of the Ummah, loving them, and being pleased with them. Whoever disparages the Companions is suspect in his religion, because they are the transmitters of the Book and the Sunnah (definition). All errors that emanated from them are forgiven due to their ijtihad (definition) (independent reasoning), their precedents, and their virtues. The killing of Uthman and Ali, may Allah be pleased with them, was an injustice, and whoever committed it or approved of it is misguided and will be held accountable by Allah.