The virtue of Lailat Al-Qadr and the Exhortation to seek it; When it is and the most likely times to seek it Sahih Muslim 1166
Arabic hadith text
حَدَّثَنَا أَبُو الطَّاهِرِ، وَحَرْمَلَةُ بْنُ يَحْيَى، قَالاَ أَخْبَرَنَا ابْنُ وَهْبٍ، أَخْبَرَنِي يُونُسُ، عَنِ ابْنِ شِهَابٍ، عَنْ أَبِي سَلَمَةَ بْنِ عَبْدِ الرَّحْمَنِ، عَنْ أَبِي هُرَيْرَةَ، - رضى الله عنه - أَنَّاللَّهِ صلى الله عليه وسلم قَالَ "أُرِيتُ لَيْلَةَ الْقَدْرِ ثُمَّ أَيْقَظَنِي بَعْضُ أَهْلِي فَنُسِّيتُهَا فَالْتَمِسُوهَا فِي الْعَشْرِ الْغَوَابِرِ " . وَقَالَ حَرْمَلَةُ " فَنَسِيتُهَا
Translation
Abu Huraira (Allah be pleased with him) reported Allah's Messenger (ﷺ) as saying
I was shown Lailat-ul-Qadr; then some members of my family awoke me up, then I was caused to forget it. So seek it in the last week. Harmala said: (The Prophet did not say:" I was made to forget," but he stated):" But I forgot it."