Musannaf Ibn Abi Shayba 33:1006

Abu Dawud Umar ibn Sa'd narrated to us, from Sufyan, from Ibn Jurayj, from Mujahid, regarding [the verse]: "The Day of Mutual Disillusion (Yawm al-Taghabun)," he said: "When the people of Paradise enter Paradise and the people of the Fire enter the Fire."