I said, "O Messenger of Allah ﷺ! What is the meaning of the white thread distinct from the black thread? Are these two threads?" He said, "You are not intelligent if you watch the two threads." He then added, "No, it is the darkness of the night and the whiteness of the day.'' (Using translation from Bukhārī 4510)
قُلْتُ يَا رَسُولَ اللهِ مَا الْخَيْطُ الْأَبْيَضُ مِنَ الْخَيْطِ الْأَسْوَدِ هُمَا الْخَيْطَانِ قَالَ «إِنَّكَ لَعَرِيضُ الْقَفَا إِنْ أَنْتَ أَبْصَرْتَ الْخَيْطَيْنِ» ثُمَّ قَالَ «لَا بَلْ هُوَ سَوَادُ اللَّيْلِ وَبَيَاضُ النَّهَارِ»