(40) باب فَضْلِ لَيْلَةِ الْقَدْرِ وَالْحَثِّ عَلَى طَلَبِهَا وَبَيَانِ مَحَلِّهَا وَأَرْجَى أَوْقَاتِ طَلَبِهَا
Ibn Umar (Allah be pleased with them) reported Allah's Messenger (ﷺ) as saying:
He who is anxious to seek it (Lailat-ul-Qadr) should seek it in the last ten (nights of Ramadan).
Reference: Sahih Muslim 1165 f
In-book reference: Book 13, Hadith 272
USC-MSA web (English) reference(deprecated numbering scheme): Book 6, Hadith 2622