Tafsir of Verse 13 in Sura 3

In Sura 3, Verse 13 , the verse in English translation is > 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. I know that the context of this verse is Battle of Badr. But who saw who twice ? The Muslims or disbelievers ?