The adhan (call to prayer) of Bilal should not prevent you from taking a meal shortly before dawn, not does the whiteness of horizon (before dawn) in this way (vertically) until it spreads out horizontally.  

قَالَ رَسُولُ اللَّهِ ﷺ لاَ يَمْنَعَنَّ مِنْ سَحُورِكُمْ أَذَانُ بِلاَلٍ وَلاَ بَيَاضُ الأُفُقِ الَّذِي هَكَذَا حَتَّى يَسْتَطِيرَ  

The Messenger of Allah ﷺ as saying: The summons (adhan) of Bilal should not restrain one of you from taking a meal shortly before dawn, for he utters adhan or calls (for prayer) so that the man at prayer may return, and the man asleep may get up. Dawn is not (the whiteness) which indicates thus (in perpendicular) - the narrator Musaddad said: Yahya joined his palms (indicating the spread of whiteness vertically - until it indicates thus - and Yahya spread out two ring-fingers of his (demonstrating the spread of whiteness horizontally)l  

قَالَ رَسُولُ اللَّهِ ﷺ لاَ يَمْنَعَنَّ أَحَدَكُمْ أَذَانُ بِلاَلٍ مِنْ سَحُورِهِ فَإِنَّهُ يُؤَذِّنُ أَوْ قَالَ يُنَادِي لِيَرْجِعَ قَائِمُكُمْ وَيَنْتَبِهَ نَائِمُكُمْ وَلَيْسَ الْفَجْرُ أَنْ يَقُولَ هَكَذَا قَالَ مُسَدَّدٌ وَجَمَعَ يَحْيَى كَفَّيْهِ حَتَّى يَقُولَ هَكَذَا وَمَدَّ يَحْيَى بِأُصْبَعَيْهِ السَّبَّابَتَيْنِ  

The Messenger of Allah ﷺ said: Eat and drink; let not the white and ascending light prevent you from (eating and drinking); so eat and drink until the red light spreads horizontally.  

قَالَ رَسُولُ اللَّهِ ﷺ كُلُوا وَاشْرَبُوا وَلاَ يَهِيدَنَّكُمُ السَّاطِعُ الْمُصْعِدُ فَكُلُوا وَاشْرَبُوا حَتَّى يَعْتَرِضَ لَكُمُ الأَحْمَرُ  

When the verse "Until the white thread of dawn appear to you distinct from its black thread" was revealed, I took a white rope and a black rope, and placed them beneath my pillow ; and then I looked at them, byt they were not clear to me. So I mentioned it to the Messenger of Allah ﷺ. He laughed and said: Your pillow is so broad and lengthy ; that is (i.e. means) night and day. The version of the narrator 'Uthman has: That is the blackness of night and whiteness of day.  

لَمَّا نَزَلَتْ هَذِهِ الآيَةُ { حَتَّى يَتَبَيَّنَ لَكُمُ الْخَيْطُ الأَبْيَضُ مِنَ الْخَيْطِ الأَسْوَدِ } قَالَ أَخَذْتُ عِقَالاً أَبْيَضَ وَعِقَالاً أَسْوَدَ فَوَضَعْتُهُمَا تَحْتَ وِسَادَتِي فَنَظَرْتُ فَلَمْ أَتَبَيَّنْ فَذَكَرْتُ ذَلِكَ لِرَسُولِ اللَّهِ ﷺ فَضَحِكَ فَقَالَ إِنَّ وِسَادَكَ لَعَرِيضٌ طَوِيلٌ إِنَّمَا هُوَ اللَّيْلُ وَالنَّهَارُ قَالَ عُثْمَانُ إِنَّمَا هُوَ سَوَادُ اللَّيْلِ وَبَيَاضُ النَّهَارِ