Musannaf Ibn Abi Shayba 27:479

Abu Usama narrated to us, he said: Muhammad bin Talha narrated to me, from Abu Ubaydah bin al-Hakam al-Azdi, raising his hadith, that the Prophet, peace and blessings of Allah be upon him, said to Ali: "You will encounter hardship after me." He said: "O Messenger of Allah, while my religion is safe?" He said: "Yes, while your religion is safe."