It was narrated from 'Adiyy bin Hatim that:

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." '

أَخْبَرَنَا عَلِيُّ بْنُ حُجْرٍ، قَالَ حَدَّثَنَا جَرِيرٌ، عَنْ مُطَرِّفٍ، عَنِ الشَّعْبِيِّ، عَنْ عَدِيِّ بْنِ حَاتِمٍ، أَنَّهُ سَأَلَ رَسُولَ اللَّهِ ﷺ عَنْ قَوْلِهِ تَعَالَى { حَتَّى يَتَبَيَّنَ لَكُمُ الْخَيْطُ الأَبْيَضُ مِنَ الْخَيْطِ الأَسْوَدِ } قَالَ " هُوَ سَوَادُ اللَّيْلِ وَبَيَاضُ النَّهَارِ " .