Thabit narrates from Abu Rafi' that he said: Abu Lu'lu'ah was the slave of al-Mughirah bin Shu'bah (may Allah be pleased with him), and he narrated the whole hadith. He says: He made a two-headed dagger for him. When Umar (may Allah be pleased with him) said the takbir, he struck him on his shoulder, then struck him in another place, and plunged the dagger into his side, and Umar (may Allah be pleased with him) fell.
The account of the killing of Umar (may Allah be pleased with him) has already passed in the established hadith from Husayn from Amr bin Maymun: that the Magian struck him with the dagger, and then whomever he passed, he stabbed those on his right and left. This is evidence that he was killed with a sharp-edged weapon; then he was washed, shrouded, and the funeral prayer was offered over him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6820