Volume 5 · Book 58 · Hadith 209
Narrated 'Abdullah: The moon was split ( into two pieces ) while we were with the Prophet in Mina. He said, "Be witnesses." Then a Piece of the moon went towards the mountain.
— Sahih Bukhari, Volume 5, Book 58: Merits of the Helpers in Madinah (Ansaar), Hadith #209