It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that he said: "I heard the Messenger of Allah (peace and blessings be upon him) during the Farewell Hajj, while he (peace and blessings be upon him) was riding his she-camel and his (peace and blessings be upon him) blessed hand was on the shoulder of Sayyiduna Ali (may Allah be pleased with him); he (peace and blessings be upon him) was saying: 'O Allah, have I conveyed (Your message)? O Allah, have I conveyed? This is my cousin and the father of my children. O Allah, whoever shows enmity to him, throw him headlong into the Fire.'"
Imam al-Tabarani (may Allah have mercy on him) said: "No one narrated this hadith from Abdullah bin Umar except Isma'il bin Yahya al-Tamimi (may Allah have mercy on him), and Muhammad bin Sahl al-Mazini (may Allah have mercy on him) is alone in narrating it."
This is how it appears in the Dar al-Haramayn printed edition, and perhaps the correct reading is (Abdullah bin Umar).