Surah At-Tawbah 9:39

إِلَّا تَنفِرُوا۟ يُعَذِّبْكُمْ عَذَابًا أَلِيمًا وَيَسْتَبْدِلْ قَوْمًا غَيْرَكُمْ وَلَا تَضُرُّوهُ شَيْـًٔا ۗ وَٱللَّهُ عَلَىٰ كُلِّ شَىْءٍ 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 Allāh is over all things competent.

Translation: Saheeh International

Tafsir

If illā lā has been assimilated with the nūn of the conditional particle in in both instances here and in the next verse you do not go forth if you do not set out with the Prophet s for the struggle He will chastise you with a painful chastisement and He will substitute you with another folk other than you that is He …

Excerpt from Tafsir al-Jalalayn, commentary on 9:39, via Quran.com. The reader has the full commentary and 9 more tafsirs.