Surah Al-Imran, ayah 13

3:13

قَدۡ كَانَ لَكُمۡ ءَايَةٞ فِي فِئَتَيۡنِ ٱلۡتَقَتَاۖ فِئَةٞ تُقَٰتِلُ فِي سَبِيلِ ٱللَّهِ وَأُخۡرَىٰ كَافِرَةٞ يَرَوۡنَهُم مِّثۡلَيۡهِمۡ رَأۡيَ ٱلۡعَيۡنِۚ وَٱللَّهُ يُؤَيِّدُ بِنَصۡرِهِۦ مَن يَشَآءُۚ إِنَّ فِي ذَٰلِكَ لَعِبۡرَةٗ لِّأُوْلِي ٱلۡأَبۡصَٰرِ ١٣

Qad kāna lakum āyatun fī fi ataynil-taqatā fi atun tuqātilu fī sabīlillāhi wa ukhrā kāfiratun yarawnahum mithlayhim ra'yal-'ayni wallāhu yu'ayyidu binasrihī man yashā'u inna fī dhālika la'ibratal li ulil-absār

Already there has been for you a sign in the two armies which met [in combat at Badr] - one fighting in the cause of Allāh and another of disbelievers. They saw them [to be] twice their [own] number by [their] eyesight.118 But Allāh supports with His victory whom He wills. Indeed in that is a lesson for those of vision.

Footnotes

118 The believers saw the disbelievers to be double their own number preceding the battle of Badr, while, in fact, they were three times their number.