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Surah 8. Al-Anfal
Ayah 17 - 19
17 فَلَمْ تَقْتُلُوهُمْ وَلَـٰكِنَّ ٱللَّهَ قَتَلَهُمْ ۚ وَمَا رَمَيْتَ إِذْ رَمَيْتَ وَلَـٰكِنَّ ٱللَّهَ رَمَىٰ ۚ وَلِيُبْلِىَ ٱلْمُؤْمِنِينَ مِنْهُ بَلَآءً حَسَنًا ۚ إِنَّ ٱللَّهَ سَمِيعٌ عَلِيمٌ
18 ذَٰلِكُمْ وَأَنَّ ٱللَّهَ مُوهِنُ كَيْدِ ٱلْكَـٰفِرِينَ
19 إِن تَسْتَفْتِحُوا۟ فَقَدْ جَآءَكُمُ ٱلْفَتْحُ ۖ وَإِن تَنتَهُوا۟ فَهُوَ خَيْرٌ لَّكُمْ ۖ وَإِن تَعُودُوا۟ نَعُدْ وَلَن تُغْنِىَ عَنكُمْ فِئَتُكُمْ شَيْـًٔا وَلَوْ كَثُرَتْ وَأَنَّ ٱللَّهَ مَعَ ٱلْمُؤْمِنِينَ
[17-19] So the fact is that you did not slay them but Allah slew them, and you did not throw (the sand) but Allah threw it.14 (And the hands of the Believers were employed for this work) so that Allah would pass the Believers successfully through this excellent test; indeed Allah is All-Hearing and All-Knowing. This is His dealing with you: as regards the disbelievers, Allah surely thwarts their evil designs. (Say to the disbelievers: ) "If you desired a decision, lo! the decision has come before you.15 It is best for you to desist from it now: but if you repeat the same folly, We will also repeat the same punishment and your forces, howsoever large their number, shall avail you nothing, for Allah is with the Believers."
14This refers to an event that happened during the Battle of Badr. After single bouts, when a general fight was going to ensue, the Holy Prophet took a handful of sand and threw it towards the army of the disbelievers, saying, "May their faces be scorched." At the same time he made a gesture and the Muslims attacked the disbelievers in a body.
15This refers to the prayer that was offered by the Quraish at the Ka'abah before they marched for the fight. The mushriks held the curtains of the Ka`abah and prayed: "O Allah! grant victory to the better of the two parties." Abu Jahl particularly invoked Allah's decision, saying, "O God! grant victory to that party which is in the right, and disgrace that one which is the aggressor. "
Accordingly Allah gave His decision and granted their prayer to the letter by giving a signal victory to the Muslims to show that they were the better of the two parties and were in the right.