انفِرُوا خِفَافًا وَثِقَالًا وَجَاهِدُوا بِأَمْوَالِكُمْ وَأَنفُسِكُمْ فِي سَبِيلِ اللَّهِ ۚ ذَٰلِكُمْ خَيْرٌ لَّكُمْ إِن كُنتُمْ تَعْلَمُونَ
“Go forth, whether light or heavy, and strive with your wealth and your lives in the cause of Allah. That is better for you, if you only knew.”
Part of Surat al-Tawba's unusually blunt command to march, read as evidence Tabuk was commanded directly by Allah.
This ayah is part of Surat al-Tawba's Tabuk-era passage addressing the hypocrites and excuse-makers who stayed behind or mocked the campaign, described at this event.