Musnad Ahmad 217:1

Sufyan narrated to us, from al-Zuhri, from Urwah, from Karz ibn Alqamah al-Khuza’i, who said: A man said: "O Messenger of Allah, does Islam have an end?" He said: "Which household?" And he said in another place: "Yes, any household of the Arabs or the non-Arabs that Allah intends good for, He introduces Islam into them." He said: "Then what?" He said: "Then tribulations will occur as if they were shadows." He said: "No, by Allah, if Allah wills." He said: "Yes, by the One in Whose hand is my soul, then you will return in them as *asawid subban*, striking the necks of one another." And it was read to Sufyan: Al-Zuhri said: "*Asawid subban*?" Sufyan said: "The black snake that rises up, meaning it lifts itself."