Sahih Muslim , Book 6, Hadith 2622 (USC-MSA) ⓘ
Ibn Umar (Allah be pleased with them) reported Allah's Messenger as saying: He who is anxious to seek it (Lailat-ul-Qadr) should seek it in the last ten (nights of Ramadan).
وَحَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، حَدَّثَنَا مُحَمَّدُ بْنُ جَعْفَرٍ، حَدَّثَنَا شُعْبَةُ، عَنْ جَبَلَةَ، قَالَ سَمِعْتُ ابْنَ عُمَرَ، - رضى الله عنهما - يُحَدِّثُ عَنِ النَّبِيِّ صلى الله عليه وسلم أَنَّهُ قَالَ " مَنْ كَانَ مُلْتَمِسَهَا فَلْيَلْتَمِسْهَا فِي الْعَشْرِ الأَوَاخِرِ " .
also referenced under: Book 13, Hadith 272 (In-Book) & Hadith 1165 (Reference)