Seek Lailat-ul-Qadr in the last week (of Ramadan).
Sahih Muslim Book 13, Hadith 268
← Previous Hadith I see that your dreams agree regarding the last week; so he who wants to seek it should seek it in the last week (during the night).

Sahih Muslim Book 13, Hadith 267 Next Hadith → I see that your dreams agree regarding the last ten (nights of Ramadan). So seek it on an odd number (of these ten nights).

Sahih Muslim Book 13, Hadith 269