Sahih Muslim Book 39, Hadith Number 6725.
Chapter : The splitting up of the Moon (a great miracle).
This hadith has been transmitted on the authority of Abdullah b. Mas’ud (who said): We were along with Allah’s Messenger (may peace be upon him) at Mina, that moon was split up into two. One of its parts was behind the mountain and the other one was on this side of the mountain. Allah’s Messenger (may peace be upon him) said to us: Bear witness to this.