This excerpt is taken from Sheikh Hafiz Mubashir Hussain Lahori's book Signs of the Day of Judgment in the Light of Authentic Hadith.
Signs of the Day of Judgment: Splitting of the Moon (The Moon Cracking):
اقْتَرَبَتِ السَّاعَةُ وَانشَقَّ الْقَمَرُ (1) وَإِن يَرَوْا آيَةً يُعْرِضُوا وَيَقُولُوا سِحْرٌ مُّسْتَمِرٌّ
"The Hour has come near, and the moon has split." If they see any miracle, they turn away saying it is an old magic that has been going on.
Reference: (Al-Qamar: 1-2)
عن أنس بن مالك رضي الله عنه أن أهل مكة سألوا النبي صلى الله عليه وسلم أن يريهم آية فأراهم انشقاق القمر مرتين
Hazrat Anas bin Malik (RA) said: "The people of Makkah demanded a miracle from the Prophet Muhammad (PBUH), so the Prophet (PBUH) showed them the moon splitting into two parts, and this happened twice."
Reference: (Bukhari: 3637, Muslim: 2800)
عن جبير بن مطعم رضي الله عنه قال انشق القمر على عهد رسول الله صلى الله عليه وسلم فصار فرقتين فرقة على هذا الحبل وفرقة على هذا الحبل فقالوا سحرنا محمد صلى الله عليه وسلم فقالوا إن كان سحرنا فإنه لا يستطيع أن يسحر الناس كلهم
Hazrat Jubair (RA) said: "During the blessed time of the Prophet Muhammad (PBUH), the moon split into two parts; one part went to this mountain and the other part went to that (other) mountain. People said that Muhammad (PBUH) has bewitched us, but his magic cannot affect all the people of the world."
Reference: (Ahmad: 116/4, Tirmidhi: 3289)
In one narration it is said:
"O Allah, be a witness."
And in another narration it is said:
"O people! Be witnesses!"
Benefits:
1. The splitting of the moon into two parts was a true event and an unparalleled miracle of the Holy Prophet Muhammad ﷺ.
2. The splitting of the moon is mentioned as a sign of the Day of Judgment.
3. The disbelievers denied it, calling it magic.
4. The splitting of the moon occurred twice.
5. This sign of the Day of Judgment has already taken place.
