Was anyone there when the Prophet ﷺ witnessed the Laylat al-Jinn?
No one was with him ﷺ that night. He disappeared, and we searched for him everywhere, fearing he had been kidnapped or killed, until at dawn we saw him coming from the direction of Hira. He told us that one of the Callers of the jinn had come to him, that a congregation was waiting for him, so he went out and recited the Qur'an to them; then he showed us the traces of their fire and campsite.
He said, "Whoever wants to come with me to be with the matter of the jinn can come," so I went with him. We walked until we reached a valley outside Makkah, and he drew a line in the sand and told me, "Sit here and do not move from this spot until I come back." He walked on reciting the Qur'an, and a whirl of black clouds gathered around him until I could no longer see him, though I could still hear his voice. When he came back after Fajr, he asked where the other group of jinn had gone, then gave them bones and animal droppings as provisions.
Every bit of bone that my ummah eats and mentions Allah's Name over shall become flesh for you.
In answer to the Muslim jinn's question of where their food would come from.