The exact night is unknown but Prophet Muhammad enjoined us to seek it in the last 10 days of the holy month.
It is a night to pray and seek the face of the Lord with various forms of Ibaadah because the reward therein is mountainous. This is why every Muslims crave to seek the night.
Allah says the night is better than 1000 months.
"The Night of Decree is better than a thousand months. The angels and the Spirit descend therein by permission of their Lord for every matter. Peace it is until the emergence of dawn."
The exact night is unknown but Prophet Muhammad enjoined us to seek it in the last 10 days of the holy month. In one of his traditions, the Prophet encouraged us to search for the night of decree in the odd numbers of the latter part of Ramadan.
However, the prophet in one or two traditions mentioned the signs of the night of majesty.
Jaabir ibn Abdullah (RA) who said: the Messenger (SAW) said: “Indeed I was shown Lailatul Qadr then I was made to forget it. It is in the last ten nights of (Ramadan) and it is a bright night, neither hot or cold. In the version of Az Zayaadee it mentions concerning the brightness of the night: “..as though there is in it the type of moon that overpowers the stars (in brightness)..” then in both versions the messenger said: “Devils on that night will not be able to come out until fajr.”
It was also reported that when Ubay ibn Ka’b was asked on another occasion ‘what are its signs’ he responded by saying “its signs are the signs that the messengers (SAW) informed us of. That the sun will rise the following morning having no rays”
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Therefore, when you observe these in the last 10 days of Ramadan, you should know the night is upon you or has passed depending on the signs you notice first.
But to be on a safe side, it is better to follow the advice of the prophet, seek it in the last 10 nights of Ramadan or in the odd nights of the holy month.