I swear by the dawn,  and by the Ten Nights,  and by the even and the odd,  and by the night when it moves away,  Is there (not) in that an oath (enough) for a man of sense?  Have you not seen how your Lord dealt with (the people) of 'Ad  of Iram, the men of tall pillars,  the like of whom were never created in the lands,  and (how He dealt) with (the people of) Thamud who had carved out the rocks in the Valley (of Qura),  and with Fir'aun (the Pharaoh), the man of the stakes,  all those who had rebelled in the cities,  and spread a lot of mischief therein.  So, your Lord unloosed on them the whip of torment.  Surely your Lord is ever on the watch.  As for man, when his Lord tests him, and thus gives him honour and bounties, he says, "My Lord has honoured me."  But when he tests him, and thus straitens his provision for him, he says, "My Lord has disgraced me."  No! But you do not honour the orphan,  and do not encourage one another to feed the needy.  And you devour the inheritance with a sweeping gulp, [I9] and love wealth, with an excessive love.  No! When the earth will be crushed thoroughly to be turned into bits,  and your Lord will come, and the angels as well, lined up in rows,  and Jahannam (Hell),on that day, will be brought forward, it will be the day when man will realise the truth, but from where will he take advantage of such realisation?  He will say, "O Would that I had sent ahead (some good deeds) for (this) my life!"  So, that day, no one can punish as He will punish,  nor can anyone shackle like He will shackle.  (As for an obedient man, it will be said to him,) "O content soul,  come back to your Lord, well-pleased, well-pleasing.  So, enter among My (special) servants,  and enter My Paradise." .
This Surah, by swearing five oaths in its beginning, emphasises the following fact:
إِنَّ رَبَّكَ لَبِالْمِرْصَادِ
Surelyyour Lord is ever on the watch. [89:14]
This means that Allah is watching over whatever you do, and reward or punishment for your deeds is certain and inevitable.
The first among the five oaths sworn at the beginning is Fajr (dawn). It may refer to the dawn of every day that brings about a great change in the world, and thus directs man's attention to the absolute Omnipotence of Allah. It is also possible that it refers to the dawn of some specific day. Commentators like Sayyidna 'Ali Ibn 'Abbas and Ibn Zubair رضي الله عنه say that the word is general, and it refers to any dawn. According to another narration of Ibn 'Abbas رضي الله عنه it refers to the dawn of the first of Muharram which is the start of the lunar-Islamic calendar. Sayyidna Qatadah رضي الله عنه among others, has interpreted it in the same way.
Some commentators, like Mujahid and 'Ikramah, refer this to the dawn of 'the Day of Sacrifice' on the tenth of Dhul Hijjah. A narration from Sayyidna Ibn 'Abbas رضي الله عنه concurs with this view. The reason for this specification is that according to Islamic principles, Allah has made a night to precede the day. All days are preceded by their respective nights, except the 'the Day of Sacrifice', because the night that precedes the Day of Sacrifice is not the night of Sacrifice. In fact, the preceding night, according to Shari'ah, is the night of 'Arafah. Staying at 'Arafat is the most important and foremost rite of Hajj. If a pilgrim is not able to reach 'Arafat on the 9th of Dhul Hijjah, any time in the day or in the night following it to halt there for a while, he will not be considered to have performed Hajj at all. However if he arrives there any time during the night before the break of dawn on the 10th of Dhul Hijjah, his halt in 'Arafah will be acceptable and his Hajj will be considered valid. This shows that the day of 'Arafah has two nights, one preceding it, and another following it. The Day of Sacrifice [10th of Dhul Hijjah] has no night. From this point of view, the dawn of the day of Sacrifice, among all the days of the year, occupies a special position. [Qurtubi].
Next, it says:
لَيَالٍ عَشْرٍ (and by the Ten Nights...89:2) According Sayyidna Ibn 'Abbas رضي الله عنه Qatadah, Mujahid, Suddi, Dahhak, Kalbi and other leading commentators, the 'ten nights' refers to the [first] ten nights of Dhul Hijjah. It is recorded in Hadith that the Holy Prophet (SM) said that, the first ten days of Dhil Hijjah are the most meritorious days for Allah's worship. Every fast of the day is equivalent to fasts of the whole year. Worshipping Allah every night during this period is equivalent to worshipping Him on the night of Qadr. [Transmitted by Tirmidhi and Ibn Majjah with a weak chain of authorities from Abu Hurairah رضي الله عنه Mazhari]. Abu-z-Zubair narrated from Sayyidna Jabir رضي الله عنه that the Holy Prophet (SM) said : وَالْفَجْرِ وَلَيَالٍ عَشْرٍ I swear by the dawn and by the Ten Nights' refers to the first ten days of Dhul Hijjah. Sayyidna Ibn 'Abbas رضي الله عنه said that these are the ten nights that are mentioned in the story of Prophet Musa عليه السلام: وَأَتْمَمْنَاهَا بِعَشْرٍ ...then We supplemented them with ten' [7:142]. Thus these are the ten nights in the whole year which are most meritorious. Imam Qurtubi says that the Hadith reported by Sayyidna Jabir رضي الله عنه indicates that the ten nights of Dhul Hijjah are most meritorious, and that the same ten nights of Dhul Hijjah were designated for Prophet Musa عليه السلام.
وَالشَّفْعِ وَالْوَتْرِ (and by the even and the odd,...89:3). The Qur'an has not specified what the words 'the even' and 'the odd' refer to. Therefore, the commentators have assigned different interpretations to them. Nevertheless, it has been mentioned in a Prophetic Hadith narrated by Abu-z-Zubair from Sayyidna Jabir رضي الله عنه thus:
'Fajr' refers to the dawn, and 'the ten nights' refer to the first ten nights of Dhul Hijjah [which include the Day of Sacrifice], and that al-watr [the odd] refers to the day of 'Arafah [because it falls on the ninth] and ash-shaf refers to the Day of Sacrifice [because it falls on the 10th day of Dhul Hijjah].'