Musnad Abu Ya'la al-Mawsili 152:2

'Abd al-Ghaffar narrated to us, 'Ali bin Mushir narrated to us, from al-A'mash, from Ibrahim, from Abu Ma'mar, from 'Abdullah, who said: While we were with the Messenger of Allah (may Allah bless him and grant him peace), the moon split into two parts. One part was behind the mountain, and one part was in front of it. The Messenger of Allah (may Allah bless him and grant him peace) said: "Bear witness."