"And We conveyed to him that matter," meaning: We informed him, "that the roots of these people," meaning their base, "would be cut off by morning."
Muhammad said: (Musbihin - by morning) is in the accusative case (nasb) as a state-of-being (hal).
﴿وقضينا إِلَيْهِ ذَلِك الْأَمر﴾ أَيْ: أَعْلَمْنَاهُ ﴿أَنَّ دَابِرَ هَؤُلاءِ﴾ أصلهم ﴿مَقْطُوع مصبحين﴾.
قَالَ محمدٌ: (مصبحين) نصبٌ على الْحَال.
