(40) باب فَضْلِ لَيْلَةِ الْقَدْرِ وَالْحَثِّ عَلَى طَلَبِهَا وَبَيَانِ مَحَلِّهَا وَأَرْجَى أَوْقَاتِ طَلَبِهَا
'Ibn 'Umar (Allah be pleased with both of them) reported Allah's Messenger (ﷺ) as saying:
Seek the time of Lailat-ul-Qadr in the last (ten nights), or he said: in the last nine (nights).
Reference: Sahih Muslim 1165 g
In-book reference: Book 13, Hadith 273
USC-MSA web (English) reference(deprecated numbering scheme): Book 6, Hadith 2623