Narrated Anas:
"The people of Makkah asked the Prophet (ﷺ) for a sign, so the moon was cleft asunder in Makkah two times (meaning two parts), so the following was revealed: 'The Hour has drawn near, and the moon has been cleft asunder, up to his saying: 'Magic, Mustamir (54:1 & 2)' meaning 'Going away.'"
English reference: Vol. 5, Book 44, Hadith 3286
Arabic reference: Book 47, Hadith 3597