Can you clarify the story of the Companion who, upon his death, said to his killer, "I have triumphed, by the Lord of the Kaaba," and who later embraced Islam?

This man is Haram ibn Milhan, the maternal uncle of Anas ibn Malik, may Allah be pleased with them both. He was one of the seventy whom the Prophet, peace and blessings be upon him, sent to teach the Quran and Sunnah, and who were betrayed and killed before reaching their destination. A man stabbed him with a spear from behind, and Haram said, "I have triumphed, by the Lord of the Kaaba."