In Musnad Al-Bazzar, it is recorded from Abu At-Tufayl 'Amir bin Wathilah from Zayd bin Harithah that the Messenger of Allah ﷺ said to Ibn Sayyad:

إِنِّي قَدْ خَبَأْتُ خَبْأً فَمَا هُوَ؟

(I am concealing something, what is it?) And the Messenger of Allah ﷺ was concealing Surat Ad-Dukhan from him. He (Ibn Sayyad) said: "It is Ad-Dukh." The Messenger of Allah ﷺ said,

اخْسَأْ مَا شَاءَ اللهُ (كَانَ)

(Be off with you! Whatever Allah wills happens.)

بِسْمِ اللَّهِ الرَّحْمَٰنِ الرَّحِيمِ 

In the Name of Allah, the Most Gracious, the Most Merciful.

حم - وَالْكِتَابِ الْمُبِينِ - إِنَّا أَنْزَلْنَاهُ فِي لَيْلَةٍ مُبَارَكَةٍ ۚ إِنَّا كُنَّا مُنْذِرِينَ - فِيهَا يُفْرَقُ كُلُّ أَمْرٍ حَكِيمٍ - أَمْرًا مِنْ عِنْدِنَا ۚ إِنَّا كُنَّا مُرْسِلِينَ - رَحْمَةً مِنْ رَبِّكَ ۚ إِنَّهُ هُوَ السَّمِيعُ الْعَلِيمُ - رَبِّ السَّمَاوَاتِ وَالْأَرْضِ وَمَا بَيْنَهُمَا ۖ إِنْ كُنْتُمْ مُوقِنِينَ - لَا إِلَٰهَ إِلَّا هُوَ يُحْيِي وَيُمِيتُ ۖ رَبُّكُمْ وَرَبُّ آبَائِكُمُ الْأَوَّلِينَ

(1. Ha Mim.)(2. By the manifest Book that makes things clear.)(3. We sent it down on a blessed night. Verily, We are ever warning.)(4. Therein (that night) is decreed every matter, Hakim.)(5. As a command from Us. Verily, We are ever sending,)(6. (As) a mercy from your Lord. Verily, He is the All-Hearer, the All-Knower.)(7. The Lord of the heavens and the earth and all that is between them, if you (but) have a faith with certainty.)(8. La ilaha illa Huwa. He gives life and causes death – your Lord and the Lord of your forefathers.)

The Qur'an was revealed on Laylatul-Qadr

Allah tells us that He revealed the Magnificent Qur'an on a blessed night, Laylatul-Qadr (the Night of Decree), as He says elsewhere:

إِنَّا أَنْزَلْنَاهُ فِي لَيْلَةِ الْقَدْرِ

(Verily, We have sent it down in the Night of Al-Qadr)(97:1). This was in the month of Ramadan, as Allah tells us:

شَهْرُ رَمَضَانَ الَّذِي أُنْزِلَ فِيهِ الْقُرْآنُ

(The month of Ramadan in which was revealed the Qur'an)(2:185). We have already quoted the relevant Hadiths in (the Tafsir of) Surat Al-Baqarah, and there is no need to repeat them here.

إِنَّا كُنَّا مُنْذِرِينَ

(Verily, We are ever warning.) means, telling them what is good for them and what is harmful for them, according to Shari'ah, so that the proof of Allah may be established against His servants.

فِيهَا يُفْرَقُ كُلُّ أَمْرٍ حَكِيمٍ 

(Therein (that night) is decreed every matter, Hakim.) means, on Laylatul-Qadr, the decrees are transferred from Al-Lawh Al-Mahfuz to the (angelic) scribes who write down the decrees of the (coming) year including life span, provision, and what will happen until the end of the year. This was narrated from Ibn 'Umar, Mujahid, Abu Malik, Ad-Dahhak and others among the Salaf.

حَكِيمٍ

(Hakim) means decided or confirmed, which cannot be changed or altered. Allah says:

أَمْرًا مِنْ عِنْدِنَا ۚ 

(As a command from Us.) meaning, everything that happens and is decreed by Allah and the revelation that He sends down – it all happens by His command, by His leave and with His knowledge.

إِنَّا كُنَّا مُرْسِلِينَ

(Verily, We are ever sending,) means, to mankind, sending Messenger who will recite to them the clear signs of Allah. The need for this was urgent.

رَحْمَةً مِنْ رَبِّكَ ۚ إِنَّهُ هُوَ السَّمِيعُ الْعَلِيمُ - رَبِّ السَّمَاوَاتِ وَالْأَرْضِ وَمَا بَيْنَهُمَا ۖ

((As) a mercy from your Lord. Verily, He is the All-Hearer, the All-Knower. The Lord of the heavens and the earth and all that is between them,) means, the One Who sent down the Qur'an is the Lord, Creator and Sovereign of the heavens and the earth and everything in between them.

إِنْ كُنْتُمْ مُوقِنِينَ

(if you (but) have a faith with certainty.) Then Allah says:

لَا إِلَٰهَ إِلَّا هُوَ يُحْيِي وَيُمِيتُ ۖ رَبُّكُمْ وَرَبُّ آبَائِكُمُ الْأَوَّلِينَ

(La ilaha illa Huwa. He gives life and causes death – your Lord and the Lord of your forefathers.) This is like the Ayah:

قُلْ يَا أَيُّهَا النَّاسُ إِنِّي رَسُولُ اللَّهِ إِلَيْكُمْ جَمِيعًا الَّذِي لَهُ مُلْكُ السَّمَاوَاتِ وَالْأَرْضِ ۖ لَا إِلَٰهَ إِلَّا هُوَ يُحْيِي وَيُمِيتُ ۖ 

(Say: "O mankind! Verily, I am sent to you all as the Messenger of Allah – to Whom belongs the dominion of the heavens and the earth. La ilaha illa Huwa. He gives life and causes death...)(7:158)