Verse 16

قُل لِّلْمُخَلَّفِينَ مِنَ ٱلْأَعْرَابِ سَتُدْعَوْنَ إِلَىٰ قَوْمٍ أُو۟لِى بَأْسٍ شَدِيدٍ تُقَـٰتِلُونَهُمْ أَوْ يُسْلِمُونَ فَإِن تُطِيعُوا۟ يُؤْتِكُمُ ٱللَّهُ أَجْرًا حَسَنًا وَإِن تَتَوَلَّوْا۟ كَمَا تَوَلَّيْتُم مِّن قَبْلُ يُعَذِّبْكُمْ عَذَابًا أَلِيمًا

Say to the sedentary amongst the Arabs, that you will be asked to face a people who possess a great might, either you fight them or they make peace, therefore, if you obey, God will give you a wonderful recompense, but if you turn away like you turned away in the past, He will make you endure a painful suffering.