Allah The Almighty Says (what means): {The angels and the Spirit descend therein by permission of their Lord for every matter. Peace it is until the emergence of dawn.} [Qur’an 97:4-5]
It is narrated on the authority of Zirr ibn Hubaysh that he heard Ubayy ibn Ka‘b  on being told that ‘Abdullaah ibn Mas‘ood had said, “He who stands for (supererogatory) prayer (every night) throughout the year, will happen to witness the Night of Al-Qadr”, commented, “By Allah except for whom there is no deity, that is in (the month of) Ramadan. (He took an unrestricted oath) By Allah, I know the night: it was the night on which The Messenger of Allah, sallallaahu ‘alaihi wa sallam, ordered us to stand in prayer, that is, the eve of the twenty-seventh day, and its sign is that the sun rises whitish on that day without having rays.” [Muslim]
According to another narration of this, “Its sign is that the sun rises in the next morning white without rays, as if it were a round tray.”  [Ibn Hibbaan]
It is also narrated on the authority of Ibn Mas‘ood  that the Prophet, sallallaahu ‘alaihi wa sallam, said: “Indeed, the Night of Al-Qadr is on the middle night of the last seven (nights) of Ramadan. The following morning, the sun rises pure without rays.” Ibn Mas‘ood  said, “I looked at it and found it just the same as described by the Messenger of Allah, sallallaahu ‘alaihi wa sallam.” [Ahmad]
It is narrated on the authority of Abu Hurairah  that the Messenger of Allah, sallallaahu ‘alaihi wa sallam, said: “The Night of Al-Qadr is on the 27th or the 29th [of Ramadan]. On that night, the angels on earth are more numerous than its pebbles.” [Ahmad]
It is narrated on the authority of ‘Ubaadah ibn As-Saamit  that the Messenger of Allah, sallallaahu ‘alaihi wa sallam, said: “Indeed, the sign of the Night of Al-Qadr is that it is bright and pure as if the moon is shining in it, still and tranquil, neither cold nor hot. On it, it is impossible for a star to be shot [at a devil] until morning comes. Its [other] sign is that in the morning after it, the sun rises brightly and without rays, similar to a full moon; and it is impossible for Satan to come out with it on that day.” [Ahmad]
It is further narrated on the authority of Jaabir  that he said: “The Messenger of Allah, sallallaahu ‘alaihi wa sallam, said: ‘I was shown (in a vision) the night of Al-Qadr, but later I forgot it. It is one of the last ten nights of Ramadan. It is shining and bright, neither hot nor cold, as if it has a full moon revealing its stars. On it the devil does not come out before its dawn rises.’” [Ibn Khuzaymah and Ibn Hibbaan]
It is narrated on the authority of Ibn ‘Abbaas  that the Prophet, sallallaahu ‘alaihi wa sallam, said, concerning the night of Al-Qadr: “It is a shining night, neither hot nor cold, and in the morning next to it the sun rises red with no rays.” [Ibn Khuzaymah]
 
Benefits and rulings

First: It is permissible for a religious scholar to hide some information that he knows if he sees that hiding it may be beneficial, just as Ibn Mas‘ood  concealed his knowledge about the Night of Al-Qadr lest the people would rely on that and slacken to stand in prayer in all the last ten nights of Ramadan.

Second: A religious scholar nevertheless has to tell the people what they need to know, just as Ubayy  told the people the date and sign of the night of Al-Qadr.

Third: It is permissible for scholars to strive their utmost, depending on their personal reasoning, and even differ about determining the benefits and evils of this. It is not forbidden so long as it is based on sound Ijtihaad (exertion of effort) and a sincere search for the truth.

Fourth: The Night of Al-Qadr is one of the last ten nights of Ramadan; most likely an odd-number night, most probably the 27th night, as Ubayy Ibn Ka‘b  took oath to that.

Fifth: These texts provide evidence for the fact that the Night of Al-Qadr has many signs, including:
1.     Angels descend on it in great numbers, led by Jibreel (Gabriel)  to witness the praying people in their mosques. Indeed, they are more numerous than pebbles. But this sign does not appear to humans.
2.     Safety and peace are widespread on it due to the acts of worship done by servants in obedience of Allah The Almighty.
3.     The next morning, the sun rises whitish without rays. The reason for that, as mentioned by religious scholars, is that the angels (who had descended on that night) then ascend to the heavens with their wings or lights screening the rays of sun due to their immense number.
4.     Among its characteristics is that it is a pure still night, neither cold nor hot, and this cold and heat are relative, depending on the climate of each country or region. The point is that it is neither cold nor hot in relation to the nights prior to and next to it.
5.     Satan does not come out with the sun of the following morning because the sun always rises between the two horns of Satan, except in the morning next to the night of Al-Qadr.

Sixth: Most of those signs mentioned above do not appear to people except after the end of the night of Al-Qadr, perchance that those who offered acts of worship on it would thank their Lord for helping them to stand in prayer and worship on it, and those who indulged on it would regret their indulgence and be determined to do their best to seize it in the coming year.

Seventh: These signs are a characteristic every Night of Qadr, past, present and future, and not specific only to the lifetime of the Prophet, sallallaahu ‘alaihi wa sallam.
Eighth: A Muslim really must strive to seize the opportunity of all the goodness that lies in it.

Article source: http://www.islamweb.net/emainpage/