إِلَّا تَنفِرُوا يُعَذِّبْكُمْ عَذَابًا أَلِيمًا وَيَسْتَبْدِلْ قَوْمًا غَيْرَكُمْ وَلَا تَضُرُّوهُ شَيْئًا ۗ وَاللَّهُ عَلَىٰ كُلِّ شَيْءٍ قَدِيرٌ
“If you do not go forth, He will punish you with a painful punishment and will replace you with another people, and you will not harm Him at all. And Allah is over all things competent.”
Part of Surat al-Tawba's unusually blunt command to march, read as evidence Tabuk was commanded directly by Allah.