Surah At-Tawbah 9:123

يَـٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوا۟ قَـٰتِلُوا۟ ٱلَّذِينَ يَلُونَكُم مِّنَ ٱلْكُفَّارِ وَلْيَجِدُوا۟ فِيكُمْ غِلْظَةً ۚ وَٱعْلَمُوٓا۟ أَنَّ ٱللَّهَ مَعَ ٱلْمُتَّقِينَ

O you who have believed, fight against those adjacent to you of the disbelievers and let them find in you harshness. And know that Allāh is with the righteous.

Translation: Saheeh International

Tafsir

O you who believe fight those of the disbelievers who are near to you that is the nearest followed by the next nearest of them and let them find harshness in you that is severity in other words be harsh with them and know that God is with the pious helping and granting them victory.

Excerpt from Tafsir al-Jalalayn, commentary on 9:123, via Quran.com. The reader has the full commentary and 9 more tafsirs.