Sunan an-Nasa'i, Volume 2, Book 13, Hadith 1365 (DarusSalam) ⓘ

It was narrated that Abu Dharr said: "We fasted Ramadan with the Messenger of Allah, and the Prophet did not lead us in Qiyam until there were seven days left of the month, then he led us in Qiyam until one-third of the night had passed. Then, when there were six days left, he did not lead us in Qiyam. When there were five days left, he led us in praying Qiyam until half the night had passed. We said: 'O Messenger of Allah (SA), why don't you lead us in praying Qiyam for the rest of the night?' He said: 'If a man prays with the Imam until he leaves, that will be continued for him as if he spent the whole night in prayer.' Then, when there were four days left, he did not lead us in praying Qiyam. When there were three days left he sent for his daughters and women, and gathered the people, and he led us in praying Qiyam until we feared that we would miss Al-Falah. Then he did not lead us in praying Qiyam for the rest of the month." Dawud (one of the narrators) said: "I said: ' What is falah?' He said: 'Sahur.'

أَخْبَرَنَا إِسْمَاعِيلُ بْنُ مَسْعُودٍ، قَالَ حَدَّثَنَا بِشْرٌ، - وَهُوَ ابْنُ الْمُفَضَّلِ - قَالَ حَدَّثَنَا دَاوُدُ بْنُ أَبِي هِنْدٍ، عَنِ الْوَلِيدِ بْنِ عَبْدِ الرَّحْمَنِ، عَنْ جُبَيْرِ بْنِ نُفَيْرٍ، عَنْ أَبِي ذَرٍّ، قَالَ صُمْنَا مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم رَمَضَانَ فَلَمْ يَقُمْ بِنَا النَّبِيُّ صلى الله عليه وسلم حَتَّى بَقِيَ سَبْعٌ مِنَ الشَّهْرِ فَقَامَ بِنَا حَتَّى ذَهَبَ نَحْوٌ مِنْ ثُلُثِ اللَّيْلِ ثُمَّ كَانَتْ سَادِسَةٌ فَلَمْ يَقُمْ بِنَا فَلَمَّا كَانَتِ الْخَامِسَةُ قَامَ بِنَا حَتَّى ذَهَبَ نَحْوٌ مِنْ شَطْرِ اللَّيْلِ قُلْنَا يَا رَسُولَ اللَّهِ لَوْ نَفَلْتَنَا قِيَامَ هَذِهِ اللَّيْلَةَ ‏.‏ قَالَ ‏ "‏ إِنَّ الرَّجُلَ إِذَا صَلَّى مَعَ الإِمَامِ حَتَّى يَنْصَرِفَ حُسِبَ لَهُ قِيَامُ لَيْلَةٍ ‏" ‏ ‏.‏ قَالَ ثُمَّ كَانَتِ الرَّابِعَةُ فَلَمْ يَقُمْ بِنَا فَلَمَّا بَقِيَ ثُلُثٌ مِنَ الشَّهْرِ أَرْسَلَ إِلَى بَنَاتِهِ وَنِسَائِهِ وَحَشَدَ النَّاسَ فَقَامَ بِنَا حَتَّى خَشِينَا أَنْ يَفُوتَنَا الْفَلاَحُ ثُمَّ لَمْ يَقُمْ بِنَا شَيْئًا مِنَ الشَّهْرِ ‏.‏ قَالَ دَاوُدُ قُلْتُ مَا الْفَلاَحُ قَالَ السُّحُورُ ‏.‏