(40) باب فَضْلِ لَيْلَةِ الْقَدْرِ وَالْحَثِّ عَلَى طَلَبِهَا وَبَيَانِ مَحَلِّهَا وَأَرْجَى أَوْقَاتِ طَلَبِهَا
Salim reported on the authority of his father that a person saw Lailat-ul- Qadr on the 27th (of Ramadan). Thereupon Allah's Apostle (ﷺ) said:
I see that your dreams agree regarding the last ten (nights of Ramadan). So seek it on an odd number (of these ten nights).
Reference: Sahih Muslim 1165 c
In-book reference: Book 13, Hadith 269
USC-MSA web (English) reference(deprecated numbering scheme): Book 6, Hadith 2619