Musannaf Ibn Abi Shayba 24:129

Abu Usama narrated to us, from Abu Sur'ah, from 'Ubadah ibn Nusayy, who said: Poetry was mentioned in the presence of the Prophet, may Allah bless him and grant him peace, and they mentioned Imru' al-Qays. The Prophet, may Allah bless him and grant him peace, said: "He is mentioned in the world, and he is mentioned in the Hereafter; the standard-bearer of the poets in Hell on the Day of Resurrection," or he said, "in the Fire."