The exact night corresponding to Laylat ul Qadr is unknown, however what is known for certain is that Laylat ul Qadr is among the last ten nights of Ramadan. Perhaps this is from the wisdom of Allah, in order for Muslims to exert their efforts throughout the last ten nights of Ramadan in the hope that Allah may accept our deeds.
The companion Ubay ibn Ka’ab says in a hadith authentically narrated by Muslim:
“By Allah, I know about laylat ul Qadr and I know it fully well that it is the twenty-seventh night (during Ramadan) on which the Messenger of Allah (pbuh) commanded us to observe prayer.”
In the Sunan of Abu Dawud Mu’awiyah (ra) narrated “The Messenger of Allah (pbuh)said regarding the night of al-Qadr It is the 27th night (of Ramadan).”
Imam Ibn Hajar comments on this hadith saying that it is most probably the saying of Mu’awiyah and not the Prophet (saw). Ibn Hajr explains that “the most likely view of the majority is that it [Laylat ul Qadr] is the 27th night of Ramadan.”
Referring to 21st, 23rd, 25th, 27th and 29th night,
Recorded by Bukhari, and narrated by `Aisha, the Prophet (pbuh) said, "Search for the Night of Qadr in the odd nights of the last ten days of Ramadan."
Narrated `Aisha and recorded in Bukhari:
Allah's Messenger (pbuh) used to practice I`tikaf in the last ten nights of Ramadan and used to say, "Look for the Night of Qadr in the last ten nights of the month of Ramadan."
The companion Abdullah Ibn Umar narrates a hadith that the scholar of Madinah, Imam Malik records in his Muwatta:
"Search for Laylat al-Qadr in the last seven days."
Abu Sa'id al-Khudri (ra) reported:
“The Prophet (pbuh) [then] came to the people and said: O people, Laylat ul Qadr was made manifest to me and I came out to inform you about it and two persons came contending with each other and there was a devil along with them and I forgot it. So seek it in the last ten nights of Ramadan. Seek it on the ninth, on the seventh and on the fifth.
I (one of the narrators) said: Abu Sa'id, you know more than us about numbers. He said: Yes, indeed we have better right than you. I said: What is this ninth, seventh, and fifth? He said: When twenty-one (nights are over) and the twenty-second begins, it is the ninth, and when twenty-three (nights) are over, that which follows (the last night) is the seventh, and when twenty-five nights are over, what follows it is fifth.”
like the narration on the authority of 'Abdullah ibn Unais (ra) in Sahih Muslim
'Abdullah b. Unais (ra) reported Allah's Messenger (pbuh) as saying:
I was shown Laylat ul Qadr; then I was made to forget it, and saw that I was prostrating in water and clay in the morning of that (night). He (the narrator) said: There was a downpour on the twenty-third night and the Messenger of Allah (pbuh) led us in prayer, and as he went back, there was a trace of water and clay on his forehead and on his nose.”
For this reason the sahaba 'Abdullah b. Unais used to say that it was the twenty-third (night).