Already there has been for you a sign in the two armies (3:13)

﴿قَدْ كَانَ لَكُمْ آيَةٌ فِي فِئَتَيْنِ الْتَقَتَا ۖ فِئَةٌ تُقَاتِلُ فِي سَبِيلِ اللَّهِ وَأُخْرَىٰ كَافِرَةٌ يَرَوْنَهُم مِّثْلَيْهِمْ رَأْيَ الْعَيْنِ ۚ وَاللَّهُ يُؤَيِّدُ بِنَصْرِهِ مَن يَشَاءُ ۗ إِنَّ فِي ذَٰلِكَ لَعِبْرَةً لِّأُولِي الْأَبْصَارِ﴾
[ آل عمران: 13]

3:13 Already there has been for you a sign in the two armies which met - one fighting in the cause of Allah and another of disbelievers. They saw them [to be] twice their [own] number by [their] eyesight. But Allah supports with His victory whom He wills. Indeed in that is a lesson for those of vision.

There was a clear sign and lesson in the two groups that met to fight in the Battle of Badr.
One group was made up of believers, and this was the Prophet ( peace be upon him ) and his Companions: they were fighting for Allah’s sake and in order to raise His Word against the word of those who disbelieve.
The other group consisted of the disbelievers of Makkah, who had come out in pride and for show.
The believers actually saw the disbelievers as being double their real number; but Allah helped His allies.
Allah gives His support to whomever He wishes.
In that there is a lesson and a warning for those of insight to realize that the help of Allah can come to the believers even though they may be few in number; and that defeat can come to those on falsehood even though they may be great in number.

There has already been a sign for you (O Jews) in the two armies that met (in combat i.e. the battle of Badr): One was fighting in the Cause of Allah, and as for the other (they) were disbelievers. They (the believers) saw them (the disbelievers) with their own eyes twice their number (although they were thrice their number). And Allah supports with His Victory whom He pleases. Verily, in this is a lesson for those who understand. (See Verse 8:44). (Tafsir At-Tabari)

phonetic Transliteration

Qad kana lakum ayatun fee fiatayni iltaqata fiatun tuqatilu fee sabeeli Allahi waokhra kafiratun yarawnahum mithlayhim raya alAAayni waAllahu yuayyidu binasrihi man yashao inna fee thalika laAAibratan liolee alabsari

Abdullah Yusuf Ali - Translation

"There has already been for you a Sign in the two armies that met (in combat): One was fighting in the cause of Allah, the other resisting Allah; these saw with their own eyes Twice their number. But Allah doth support with His aid whom He pleaseth. In this is a warning for such as have eyes to see."

Safi-ur-Rahman al-Mubarakpuri

There has already been a sign for you in the two armies that met. One was fighting in the cause of Allah, and as for the other, in disbelief. They saw them with their own eyes twice their number. And Allah supports with His aid whom He wills. Verily, in this is a lesson for those who understand.

Page 51 English transliteration