" Until the white streak of the dawn becomes distinct from the dark streak" (ii. 187) Adi b. Hatim said: Messenger of Allah, verily I keep underneath my pillow two strings, one white and the other black, by which I distinguish night from dawn. Upon this the Messenger of Allah ﷺ said: Your pillow seems to be very large. For the word khait implies the blackness of the night and the whiteness of the dawn.  

لَمَّا نَزَلَتْ { حَتَّى يَتَبَيَّنَ لَكُمُ الْخَيْطُ الأَبْيَضُ مِنَ الْخَيْطِ الأَسْوَدِ مِنَ الْفَجْرِ} قَالَ لَهُ عَدِيُّ بْنُ حَاتِمٍ يَا رَسُولَ اللَّهِ إِنِّي أَجْعَلُ تَحْتَ وِسَادَتِي عِقَالَيْنِ عِقَالاً أَبْيَضَ وَعِقَالاً أَسْوَدَ أَعْرِفُ اللَّيْلَ مِنَ النَّهَارِ فَقَالَ رَسُولُ اللَّهِ ﷺ إِنَّ وِسَادَتَكَ لَعَرِيضٌ إِنَّمَا هُوَ سَوَادُ اللَّيْلِ وَبَيَاضُ النَّهَارِ  

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  

"When 'Until the white (light) thread of dawn appears distinct to you from the black thread (of night)' was revealed, the Prophet ﷺ said to me: 'That only refers to the whiteness of the day from the blackness of the night.'" (Using translation from Tirmidhī 2970)   

لَمَّا نَزَلَتْ {وَكُلُوا وَاشْرَبُوا حَتَّى يَتَبَيَّنَ لَكُمُ الْخَيْطُ الْأَبْيَضُ مِنَ الْخَيْطِ الْأَسْوَدِ} قَالَ النَّبِيُّ ﷺ «إِنَّمَا ذَلِكَ بَيَاضُ النَّهَارِ وَسَوَادُ اللَّيْلِ»  

("الخَيطُ الأبْيَضُ منَ الخَيط الأسْوَد من الفَجْرِ انمَّا هُمَا سَوادُ اللَّيل وبياضُ النَّهار".