if one of them went to sleep before eating supper, it was not permissible for him to eat or drink anything that night or the following day, until the sun had set. (That continued) until this Verse was revealed: "And eat and drink until the white thread (light) of dawn appears to you distinct from the black thread (darkness of night)." He said: "This was revealed concerning Abu Qais bin 'Amr who came to his family after Maghrib when he was fasting, and said: 'Is there anything to eat?" His wife said: 'No , but I will go out, and he lay down and slept. She came back and found him sleeping, so she woke him up, but he did not eat anything. He spent the night fasting and woke up the next day fasting, until he passed out at midday. That was before this Verse was revealed, and Allah revealed it concerning him." '  

أَنْ يَأْكُلَ شَيْئًا وَلاَ يَشْرَبَ لَيْلَتَهُ وَيَوْمَهُ مِنَ الْغَدِ حَتَّى تَغْرُبَ الشَّمْسُ حَتَّى نَزَلَتْ هَذِهِ الآيَةُ { وَكُلُوا وَاشْرَبُوا } إِلَى { الْخَيْطِ الأَسْوَدِ } قَالَ وَنَزَلَتْ فِي أَبِي قَيْسِ بْنِ عَمْرٍو أَتَى أَهْلَهُ وَهُوَ صَائِمٌ بَعْدَ الْمَغْرِبِ فَقَالَ هَلْ مِنْ شَىْءٍ فَقَالَتِ امْرَأَتُهُ مَا عِنْدَنَا شَىْءٌ وَلَكِنْ أَخْرُجُ أَلْتَمِسُ لَكَ عَشَاءً فَخَرَجَتْ وَوَضَعَ رَأْسَهُ فَنَامَ فَرَجَعَتْ إِلَيْهِ فَوَجَدَتْهُ نَائِمًا وَأَيْقَظَتْهُ فَلَمْ يَطْعَمْ شَيْئًا وَبَاتَ وَأَصْبَحَ صَائِمًا حَتَّى انْتَصَفَ النَّهَارُ فَغُشِيَ عَلَيْهِ وَذَلِكَ قَبْلَ أَنْ تَنْزِلَ هَذِهِ الآيَةُ فَأَنْزَلَ اللَّهُ فِيهِ  

he asked the Messenger of Allah about the verse "Until the white thread (light) of dawn appears to you distinct from the black thread (darkness of night)." He said: "It is the blackness of the night and the whiteness of the day." '  

أَنَّهُ سَأَلَ رَسُولَ اللَّهِ ﷺ عَنْ قَوْلِهِ تَعَالَى { حَتَّى يَتَبَيَّنَ لَكُمُ الْخَيْطُ الأَبْيَضُ مِنَ الْخَيْطِ الأَسْوَدِ } قَالَ هُوَ سَوَادُ اللَّيْلِ وَبَيَاضُ النَّهَارِ