Language:
كتاب فضل ليلة القدر
32
Virtues of the Night of Qadr
(2)
Chapter: To look for the night of Qadr in the last seven nights (of Ramadan)
(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).

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، أَخْبَرَنَا مَالِكٌ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ ـ رضى الله عنهما ـ أَنَّ رِجَالاً، مِنْ أَصْحَابِ النَّبِيِّ صلى الله عليه وسلم أُرُوا لَيْلَةَ الْقَدْرِ فِي الْمَنَامِ فِي السَّبْعِ الأَوَاخِرِ، فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ أَرَى رُؤْيَاكُمْ قَدْ تَوَاطَأَتْ فِي السَّبْعِ الأَوَاخِرِ، فَمَنْ كَانَ مُتَحَرِّيَهَا فَلْيَتَحَرَّهَا فِي السَّبْعِ الأَوَاخِرِ ‏"‏‏.‏
Reference : Sahih al-Bukhari 2015
In-book reference : Book 32, Hadith 2
USC-MSA web (English) reference : Vol. 3, Book 32, Hadith 232
  (deprecated numbering scheme)