Musannaf Ibn Abi Shayba 37:359

Waki’ narrated to us, from ‘Abd al-Hamid ibn Bahram, from Shahr ibn Hawshab, from Asma’ bint Yazid, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "There is no harm upon you from him. If he emerges while I am alive, then I am his adversary. And if he emerges after my death, then Allah is my successor over every Muslim."