The Messenger of Allah feared that the Ansar might think that they are not obliged to support him except from his enemies who attack Al-Madinah, not to march with him to an enemy in other areas. When the Prophet said this, Sa`d bin Mu`adh asked him, `O Allah's Messenger! فَلَمْ تَقْتُلُوهُمْ وَلَـكِنَّ اللَّهَ قَتَلَهُمْ. (You killed them not, but Allah killed them.) meaning, it is not because of your power and strength that you killed the pagans, who were many while you were few. Rather, it is He Who gave you victory over them, just as He said in another Ayah, It was not you ˹believers˺ who killed them, but it was Allah Who did so. Nor was it you ˹O Prophet˺ who threw ˹a handful of sand at the disbelievers˺, 1 but it was Allah Who did so, rendering the believers a great favour. Surely Allah is All-Hearing, All-Knowing. Tafseer Tafheem-ul-Quran Syed Abu-al-A'la Maududi. (8:17) So the fact is that it was not you, but it was Allah Who killed them; and it was not you when you threw [sand at them], but it was Allah Who threw it, *14 (and the believers were employed for the task) that He might cause the believers to successfully pass through this test. Vay Tiền Trả Góp 24 Tháng.

tafsir surah al anfal ayat 17