Musnad Ahmad 7:31

Sufyan narrated to us, Amr said: And I heard Ikrimah [regarding the verse]: "And [mention, O Muhammad], when We directed toward you a group of the jinn, listening to the Qur'an" [Al-Ahqaf: 29]. And it was read to Sufyan, from Al-Zubayr: "A group of the jinn listening to the Qur'an," he said: "At Nakhlah, and the Messenger of Allah, peace and blessings of Allah be upon him, was praying the late night prayer (Isha), 'they almost became upon him a compacted mass' [Al-Jinn: 19]." Sufyan said: "The *lubad* (compacted mass): some of them upon others, like felt (labad) [layered] one upon another."