(3) باب تَحَرِّي لَيْلَةِ الْقَدْرِ فِي الْوِتْرِ مِنَ الْعَشْرِ الأَوَاخِرِ
Narrated Ibn `Abbas:
The Prophet (ﷺ) said, "Look for the Night of Qadr in the last ten nights of Ramadan ,' on the night when nine or seven or five nights remain out of the last ten nights of Ramadan (i.e. 21, 23, 25, respectively).
Reference: Sahih al-Bukhari 2021
In-book reference: Book 32, Hadith 8
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 3, Book 32, Hadith 238