A’ishah (radiyallahu anha) reports that Rasulullah (sallallahu alaihi wasallam) said: “Seek laylatal qadr among the odd numbered nights of the last ten days of the month of Ramadan.”
Note: According to the great majority of the religious scholars, the last ten nights cmmence on the 21st night. Such is the case whether the month of Ramadan consists of 29 days or 30. So, one should seek Laylatal Qadr on the 21st, 23rd, 25th, 27th and 29th night.
Ibn Hazm has a different opinion, saying that the word “asharah” used in the Hadith means ten. As such, the above calculation will only be correct in cases where the month of Ramadan consists of thirty days. However, when there are only twenty nine days in the month ( as often happens), the last ten days will commence with the 19th day, and the night being the 20th night. According to this calculation, it would appear that the unevenly numbered nights will actually be the 20th, 22nd, 24th, 26th, 28th and 30th nights.
But all Ulama agree that when in search of laylatal qadr Rasulullah (sallallahu alaihi wasallam) went into Itikaf, he commenced it on the 21st night of Ramadan. In view of this, these Ulama consider the odd nights to be the appropriate nights for laylatal qadr.
One should, therefore, spend each and every night from the 20th onwards in worship of Allah. So that one may be sure of having got the barakah of Ramadan. Spending ten or eleven nights in devotion is definitely not so difficult, if one looks at the great reward that is promised.