Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
quran:9:123 –

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

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.
القرآن:٩:١٢٣ –

يَا أَيُّهَا الَّذِينَ آمَنُوا قَاتِلُوا الَّذِينَ يَلُونَكُمْ مِنَ الْكُفَّارِ وَلْيَجِدُوا فِيكُمْ غِلْظَةً ۚ وَاعْلَمُوا أَنَّ اللَّهَ مَعَ الْمُتَّقِينَ  

{يا أيها الذين آمنوا قاتلوا الذين يلونكم من الكفار} أي الأقرب فالأقرب منهم {وليجدوا فيكم غلظة} شدة، أي أغلظوا عليهم {واعلموا أن الله مع المتقين} بالعون والنصر.