"In days of misfortune," meaning: ominous/unfortunate, and they are the eight days mentioned in [Surat] al-Haqqah, the first of which was Wednesday until the following Wednesday.
Muhammad said: The reading of Nafi' is (Nahsat) with the sukun on the Ha'. The singular of it is Nahs. The meaning is: they are [days of] misfortune upon them.
Interpretation of Surat Fussilat from verse 17 to verse 20.
﴿فِي أَيَّام نحسات﴾ أَي: مشئومات , وَهِي الثَّمَانِية الْأَيَّام الَّتِي فِي الحاقة , كَانَ أَولهَا يَوْم الْأَرْبَعَاء إِلَى الْأَرْبَعَاء الآخر.
قَالَ محمدٌ: قِرَاءَة نَافِع (نحْسات) بتسكين الْحَاء , وَاحِدهَا نَحْسٌ الْمَعْنى: هِيَ نحسات عَلَيْهِم.
تَفْسِير سُورَة فصلت من الْآيَة ١٧ إِلَى آيَة ٢٠.
