Musnad Ahmad 30:1364

Yunus narrated to us, Laith narrated to us, from Muhammad, from al-Qa'qa' ibn Hakim, from Abu Salih, from Abu Hurairah, from the Messenger of Allah, may Allah bless him and grant him peace, that he said: "A group will not cease to be upon this matter, [remaining] upon the truth. Those who oppose them will not harm them, until the command of Allah comes to them, while they are [still] upon that."