Who was Abdur-Rahmaan ibn Muljam? Was he the cousin of Prophet Muhammad, sallallaahu 'alayhi wa sallam? What wrong had he done?

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.

Abdur-Rahmaan ibn Muljam Al-Muraadi Al-Himyari lived part of his life during the Jaahiliyyah (Pre-Islamic Era), and he migrated during the Caliphate of ‘Umar . He studied at the hands of Mu’aath ibn Jabal and he was among the reciters and the people of Fiqh and worship.

He was one of the supporters of ‘Ali ibn Abi Taalib and he witnessed the battle of Siffeen with him. Then he turned against him and vowed to kill him, so he stabbed him in Kufah during the Fajr prayer and killed him.

This is what was mentioned about his biography in the Book of Al-A’laam by Az-Zirikli. Hence, you should know that he was from Himyar, while the Prophet was from Quraysh, so he was not one of his cousins.

One of his grievous sins was his murder of the Commander of the Faithful (Ali ), and he was the most wretched tyrant of this nation, as it is stated in the hadeeth reported by At-Tabaraani and others that the most wretched tyrant of the former people was the one who killed the camel of Prophet Saalih and the most wretched tyrant of the later people was the one who killed ‘Ali .

This hadeeth was classified as saheeh (sound) by Al-Albaani in As-Silsilah As-Saheehah.

Therefore, it was only the one who was killed (‘Ali ) who was the cousin of the Prophet .

Allah knows best.