(2) باب الْتِمَاسِ لَيْلَةِ الْقَدْرِ فِي السَّبْعِ الأَوَاخِرِ
Narrated Ibn `Umar:
Some men amongst the companions of the Prophet (ﷺ) were shown in their dreams that the night of Qadr was in the last seven nights of Ramadan. Allah's Messenger (ﷺ) said, "It seems that all your dreams agree that (the Night of Qadr) is in the last seven nights, and whoever wants to search for it (i.e. the Night of Qadr) should search in the last seven (nights of Ramadan).
Reference: Sahih al-Bukhari 2015
In-book reference: Book 32, Hadith 2
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 3, Book 32, Hadith 232