Musnad Ahmad 26:809

Abu Mu'awiyah narrated to us, Al-A'mash narrated to us, from Ibrahim, from Abu Ma'mar, from Abdullah, who said: The moon split while we were with the Prophet, may Allah bless him and grant him peace, at Mina, until a portion of it went behind the mountain. He said: Then the Messenger of Allah, may Allah bless him and grant him peace, said: "Bear witness."