Surat Al Anfal: (17-18)

{فَلَمْ تَقْتُلُوهُمْ وَلَـكِنَّ اللّهَ قَتَلَهُمْ وَمَا رَمَيْتَ إِذْ رَمَيْتَ وَلَـكِنَّ اللّهَ رَمَى وَلِيُبْلِيَ الْمُؤْمِنِينَ مِنْهُ بَلاء حَسَناً إِنَّ اللّهَ سَمِيعٌ عَلِيمٌ} [الأنفال : 17]

17- So, you did not kill them by your power because your number was few and their number was large, but Allah killed them by the angels whom He sent and by throwing horror in their hearts.

The Messenger of Allah (peace be upon him) picked up a handful of sand and throw it in the face of polytheists and sand got into their eyes as Al Haythamy graded it as authentic in Majma` Az-Zawa'id from the narration of At-Tabarany.

Allah (Glory be to Him) said which means: O Prophet, it was not you who throw sands in the eyes of polytheists, but Allah did by putting sand in their eyes to defeat them and bestow His Victory and the booty over the believers and so that you would know His Rights to thank Him and be grateful. Indeed, Allah is All-Responding to your invocations and seeking for help, and knowing of your intentions and your conditions.

{ذَلِكُمْ وَأَنَّ اللّهَ مُوهِنُ كَيْدِ الْكَافِرِينَ} [الأنفال : 18]

18- That was the good efforts of the believers, and Allah weakens the plots and tricks of the disbelievers until you have victory over them.