Narrated Ibn Mas'ud:
"The moon was cleft asunder during the time of the Messenger of Allah (ﷺ), so the Prophet (ﷺ) said to us: 'Bear witness.'" (ID)
English reference (ID): Vol. 5, Book 44, Hadith 3287 (ID)
Arabic reference (ID): Book 47, Hadith 3598 (ID)