Sahih Muslim , Book 13, Hadith 268 (In-Book) ⓘ
Ibn 'Umar (Allah be pleased with them) reported Allah's Apostle as saying: Seek Lailat-ul-Qadr in the last week (of Ramadan).
وَحَدَّثَنَا يَحْيَى بْنُ يَحْيَى، قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنِ ابْنِ، عُمَرَ - رضى الله عنهما - عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " تَحَرَّوْا لَيْلَةَ الْقَدْرِ فِي السَّبْعِ الأَوَاخِرِ " .
also referenced under: Hadith 1165 (Reference) & Book 6, Hadith 2618 (USC-MSA)