Hadithcore
Musnad Ahmad 4270
graded· 4864

It was narrated from ‘Abdullah that

He said concerning this verse: “The Hour has drawn near, and the moon has been cleft asunder” (al-Qamar 54:1): It was split at the time of the Messenger of Allah (ﷺ) into two halves, one half was behind the mountain and the other one half was over the mountain. And The Messenger of Allah (ﷺ) said: "O Allah, bear witness."

References1 variant
Arabic/English book
Book 26, Hadith 4270