Sahih Muslim Book - 6, Hadith - 1785

حَدَّثَنَا مُحَمَّدُ بْنُ مِهْرَانَ الرَّازِىُّ حَدَّثَنَا الْوَلِيدُ بْنُ مُسْلِمٍ حَدَّثَنَا الأَوْزَاعِىُّ حَدَّثَنِى عَبْدَةُ عَنْ زِرٍّ قَالَ سَمِعْتُ أُبَىَّ بْنَ كَعْبٍ يَقُولُ - وَقِيلَ لَهُ إِنَّ عَبْدَ اللَّهِ بْنَ مَسْعُودٍ يَقُولُ مَنْ قَامَ السَّنَةَ أَصَابَ لَيْلَةَ الْقَدْرِ - فَقَالَ أُبَىٌّ وَاللَّهِ الَّذِى لاَ إِلَهَ إِلاَّ هُوَ إِنَّهَا لَفِى رَمَضَانَ - يَحْلِفُ مَا يَسْتَثْنِى - وَوَاللَّهِ إِنِّى لأَعْلَمُ أَىُّ لَيْلَةٍ هِىَ. هِىَ اللَّيْلَةُ الَّتِى أَمَرَنَا بِهَا رَسُولُ اللَّهِ -صلى الله عليه وسلم- بِقِيَامِهَا هِىَ لَيْلَةُ صَبِيحَةِ سَبْعٍ وَعِشْرِينَ وَأَمَارَتُهَا أَنْ تَطْلُعَ الشَّمْسُ فِى صَبِيحَةِ يَوْمِهَا بَيْضَاءَ لاَ شُعَاعَ لَهَا.

It was narrated that Zirr said: "I heard Ubayy bin Ka'b say - when it was said to him that 'Abdullah bin Mas'ud was saying that whoever prays Qiyam for a year will attain Lailat Al-Qadr : 'By Allah, besides Whom there is none worthy of worship! It is in Ramadan' - and he swore with no reservation - 'and by Allah, I know which night it is! It is the night which the Messenger of Allah (s.a.w) commanded us to spend in prayer; it is the night of the twenty-seventh, and its sign is that the sun rises that day bright with no rays."'