When the above verses were revealed: 'Until the white thread appears to you, distinct from the black thread,' I took two (hair) strings, one black and the other white, and kept them under my pillow and went on looking at them throughout the night but could not make anything out of it. So, the next morning I went to Messenger of Allah ﷺ and told him the whole story. He explained to me, "That verse means the darkness of the night and the whiteness of the dawn."  

لَمَّا نَزَلَتْ {حَتَّى يَتَبَيَّنَ لَكُمُ الْخَيْطُ الأَبْيَضُ مِنَ الْخَيْطِ الأَسْوَدِ} عَمَدْتُ إِلَى عِقَالٍ أَسْوَدَ وَإِلَى عِقَالٍ أَبْيَضَ فَجَعَلْتُهُمَا تَحْتَ وِسَادَتِي فَجَعَلْتُ أَنْظُرُ فِي اللَّيْلِ فَلاَ يَسْتَبِينُ لِي فَغَدَوْتُ عَلَى رَسُولِ اللَّهِ ﷺ فَذَكَرْتُ لَهُ ذَلِكَ فَقَالَ إِنَّمَا ذَلِكَ سَوَادُ اللَّيْلِ وَبَيَاضُ النَّهَارِ  

When the following verses were revealed: 'Eat and drink until the white thread appears to you, distinct from the black thread' and of dawn was not revealed, some people who intended to fast, tied black and white threads to their legs and went on eating till they differentiated between the two. Allah then revealed the words, 'of dawn', and it became clear that meant night and day.  

أُنْزِلَتْ {وَكُلُوا وَاشْرَبُوا حَتَّى يَتَبَيَّنَ لَكُمُ الْخَيْطُ الأَبْيَضُ مِنَ الْخَيْطِ الأَسْوَدِ} وَلَمْ يَنْزِلْ مِنَ الْفَجْرِ فَكَانَ رِجَالٌ إِذَا أَرَادُوا الصَّوْمَ رَبَطَ أَحَدُهُمْ فِي رِجْلِهِ الْخَيْطَ الأَبْيَضَ وَالْخَيْطَ الأَسْوَدَ وَلَمْ يَزَلْ يَأْكُلُ حَتَّى يَتَبَيَّنَ لَهُ رُؤْيَتُهُمَا فَأَنْزَلَ اللَّهُ بَعْدُ {مِنَ الْفَجْرِ} فَعَلِمُوا أَنَّهُ إِنَّمَا يَعْنِي اللَّيْلَ وَالنَّهَارَ  

My father said that Allah s Apostle said, "Bilal pronounces 'Adhan at night, so keep on eating and drinking (Suhur) till Ibn Um Maktum pronounces Adhan." Salim added, "He was a blind man who would not pronounce the Adhan unless he was told that the day had dawned."  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ إِنَّ بِلاَلاً يُؤَذِّنُ بِلَيْلٍ فَكُلُوا وَاشْرَبُوا حَتَّى يُنَادِيَ ابْنُ أُمِّ مَكْتُومٍ ثُمَّ قَالَ وَكَانَ رَجُلاً أَعْمَى لاَ يُنَادِي حَتَّى يُقَالَ لَهُ أَصْبَحْتَ أَصْبَحْتَ  

Bilal used to pronounce the Adhan at night, so Messenger of Allah ﷺ? said, "Carry on taking your meals (eat and drink) till Ibn Um Maktum pronounces the Adhan, for he does not pronounce it till it is dawn.  

رَسُولُ اللَّهِ ﷺ كُلُوا وَاشْرَبُوا حَتَّى يُؤَذِّنَ ابْنُ أُمِّ مَكْتُومٍ فَإِنَّهُ لاَ يُؤَذِّنُ حَتَّى يَطْلُعَ الْفَجْرُ قَالَ الْقَاسِمُ وَلَمْ يَكُنْ بَيْنَ أَذَانِهِمَا إِلاَّ أَنْ يَرْقَى ذَا وَيَنْزِلَ ذَا  

The Prophet ﷺ said, "The Adhan pronounced by Bilal should not stop you from taking Suhur, for he pronounces the Adhan at night, so that the one offering the late night prayer (Tahajjud) from among you might hurry up and the sleeping from among you might wake up. It does not mean that dawn or morning has started." Then he (the Prophet) pointed with his fingers and raised them up (towards the sky) and then lowered them (towards the earth) like this (Ibn Masʿud imitated the gesture of the Prophet). Az-Zuhri gestured with his two index fingers which he put on each other and then stretched them to the right and left. These gestures illustrate the way real dawn appears. It spreads left and right horizontally. The dawn that appears in the high sky and lowers down is not the real dawn) .  

عَنِ النَّبِيِّ ﷺ قَالَ لاَ يَمْنَعَنَّ أَحَدَكُمْ أَوْ أَحَدًا مِنْكُمْ أَذَانُ بِلاَلٍ مِنْ سَحُورِهِ فَإِنَّهُ يُؤَذِّنُ أَوْ يُنَادِي بِلَيْلٍ لِيَرْجِعَ قَائِمَكُمْ وَلِيُنَبِّهَ نَائِمَكُمْ وَلَيْسَ أَنْ يَقُولَ الْفَجْرُ أَوِ الصُّبْحُ وَقَالَ بِأَصَابِعِهِ وَرَفَعَهَا إِلَى فَوْقُ وَطَأْطَأَ إِلَى أَسْفَلُ حَتَّى يَقُولَ هَكَذَا وَقَالَ زُهَيْرٌ بِسَبَّابَتَيْهِ إِحْدَاهُمَا فَوْقَ الأُخْرَى ثُمَّ مَدَّهَا عَنْ يَمِينِهِ وَشِمَالِهِ