Narrated Anas bin Malik: The people of Mecca asked Allah's Apostle to show them a miracle. So he showed them the moon split in two halves between which they saw the Hira' mountain.
Hadith Referenceصحيح البخاري / كتاب مناقب الأنصار / 3868
Hadith Gradingمحدثین:أحاديث صحيح البخاريّ كلّها صحيحة
´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.'"
Shaykh Dr. Abdur Rahman Freywai
Explanation: 1: In this hadith, the meaning of "martayn" is not that the incident of the moon splitting occurred twice. This incident did not happen twice, it happened only once. Here, "martayn" refers to "two pieces" only.
Source: Sunan al-Tirmidhi – Majlis ‘Ilmi Dar al-Da‘wah, New Delhi Edition, Page: 3286