Musannaf Ibn Abi Shayba 3:6315

Waki’ narrated to us, he said: Sufyan narrated to us, from Ibn Abi Najih, from Mujahid, regarding [the verse]: "Indeed, We sent it down in the Night of Decree," he said: The Night of Judgment. "And what can make you know what the Night of Decree is?" He said: The Night of Judgment.