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'Abdullah b. Mas'ud reported that the moon was split up in two parts during the lifetime of Allah's Messenger (ﷺ). The mountain covered one of its parts and one part of it was above the mountain and Allah's Messenger (ﷺ) said: Bear witness to this.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُعَاذٍ الْعَنْبَرِيُّ، حَدَّثَنَا أَبِي، حَدَّثَنَا شُعْبَةُ، عَنِ الأَعْمَشِ، عَنْ إِبْرَاهِيمَ، عَنْ أَبِي مَعْمَرٍ، عَنْ عَبْدِ اللَّهِ بْنِ مَسْعُودٍ، قَالَ انْشَقَّ الْقَمَرُ عَلَى عَهْدِ رَسُولِ اللَّهِ صلى الله عليه وسلم فِلْقَتَيْنِ فَسَتَرَ الْجَبَلُ فِلْقَةً وَكَانَتْ فِلْقَةٌ فَوْقَ الْجَبَلِ فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " اللَّهُمَّ اشْهَدْ " .
sunnah.com