Praise be to Allaah.  

Firstly: 

There are reports which speak of the great virtue of doing acts of worship on Laylat al-Qadr. Our Lord, may He be blessed and exalted, has told us that it is better than a thousand nights, and the Prophet (peace and blessings of Allaah be upon him) said that whoever spends this night in prayer out of faith and in the hope of reward will be forgiven his previous sins. 

Allaah says (interpretation of the meaning): 

“Verily, We have sent it (this Qur’aan) down in the Night of Al‑Qadr (Decree).

2. And what will make you know what the Night of Al‑Qadr (Decree) is?

3. The Night of Al‑Qadr (Decree) is better than a thousand months (i.e. worshipping Allaah in that night is better than worshipping Him a thousand months, i.e. 83 years and 4 months).

4. Therein descend the angels and the Rooh [Jibreel (Gabriel)] by Allaah’s Permission with all Decrees,

5. (All that night), there is peace (and goodness from Allaah to His believing slaves) until the appearance of dawn”

[al-Qadr 97:1-5] 

And it was narrated from Abu Hurayrah (may Allaah be pleased with him) that the Prophet (peace and blessings of Allaah be upon him) said: “Whoever spends this night in prayer out of faith and in the hope of reward will be forgiven his previous sins.” Narrated by al-Bukhaari, 1901; Muslim, 760. 

Out of faith means believing in its virtue and in the reward for that. 

In the hope of reward means by seeking the pleasure of Allaah. 

Secondly: 

The scholars differed as to the definition of Laylat al-Qadr, and there are many opinions, more than forty as it says in Fath al-Baari. The most likely to be correct is the view that it is one of the odd-numbered nights among the last ten nights of Ramadaan. 

It was narrated from ‘Aa’ishah (may Allaah be pleased with her) that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Seek Laylat al-Qadr among the odd numbered nights of the last ten nights of Ramadaan.” Narrated by al-Bukhaari, 2017; Muslim, 1169. 

Al-Bukhaari included this hadeeth in a chapter entitled: “Seeking Laylat al-Qadr among the odd numbered nights of the last ten nights (of Ramadaan).” 

The reason why it is hidden is to encourage the Muslim to strive hard in worship and du’aa’ and dhikr during all the last ten nights of Ramadaan. This is the same reason why the time when du’aa’ is answered on Friday has not been defined, and why the ninety-names of Allaah have not been defined, concerning which the Prophet (peace and blessings of Allaah be upon him) said: “Whoever learns them by heart will enter Paradise.” Narrated by al-Bukhaari, 2736; Muslim, 2677. 

Al-Haafiz Ibn Hajar (may Allaah have mercy on him) said: 

The words of Imam al-Bukhaari (may Allaah have mercy on him) – “Seeking Laylat al-Qadr among the odd numbered nights of the last ten nights (of Ramadaan)” – indicate that it is most likely that Laylat al-Qadar cannot be in any month other than Ramadaan, and is in the last ten nights thereof, and is one of the odd-numbered nights, but not on any particular night. This is what is indicated by a number of the reports that have been narrated concerning it. 

Fath al-Baari, 4/260. 

And he said: 

The scholars said: The reason why Laylat al-Qadar has been concealed is so that people will strive to seek it, because if its timing was known, they would limit their efforts to that night only, as we have explained previously about the time on Friday (when du’aa’s are answered). 

Fath al-Baari, 4/266. 

Thirdly: 

Based on this, it is not possible for anyone to be certain that a particular night is Laylat al-Qadr, especially since we know that the Prophet (peace and blessings of Allaah be upon him) wanted to tell his ummah when it was, then he told them that Allaah had taken away that knowledge. 

It was narrated from ‘Ubaadah ibn al-Saamit (may Allaah be pleased with him) that the Messenger of Allaah (peace and blessings of Allaah be upon him) came out with the news of Laylat al-Qadr, but two men among the Muslims started arguing. He said: “I came out to tell you about Laylat al-Qadr, but So and so and So and so started arguing, so (that knowledge) was taken away. Perhaps that will be better for you. So seek it on the (twenty-) seventh and the (twenty-) ninth and the (twenty-) fifth.” Narrated by al-Bukhaari, 49. 

The scholars of the Standing Committee said: 

With regard to singling out one night of Ramadaan as Laylat al-Qadr, this requires evidence to show that it is this night and not any other. But the odd numbered nights of the last ten nights of Ramadaan are more likely than others (to be Laylat al-Qadr) and the twenty-seventh night is the most likely night to be Laylat al-Qadr, because of the ahaadeeth to that effect. 

Fataawa al-Lajnah al-Daa’imah li’l-Buhooth al-‘Ilmiyyah wa’l-Ifta’, 10/413 

Hence the Muslim should not assume that any particular night is Laylat al-Qadr, because that would mean that he is being certain about something concerning which we cannot be certain, and because it means that he is missing out on something that is good for him. It may be the night of the twenty-first, or the twenty-third, or the twenty-ninth. If he spends the night of the twenty-seventh only in prayer, then he will have missed out on a lot of goodness, and he may have missed that blessed night. 

The Muslim should strive his hardest to do acts of obedience and worship throughout Ramadaan, and more so in the last ten days. This is the teaching of the Prophet (peace and blessings of Allaah be upon him).  

It was narrated that ‘Aa’ishah (may Allaah be pleased with her) said: When the last ten days of Ramadaan began, the Prophet (peace and blessings of Allaah be upon him) would tighten his waist-wrapper, spend his nights in prayer, and wake his family.

Narrated by Muslim, 2024; Muslim, 1174. 

And Allaah knows best.