ENOfficial
Narrated Al-Bara: I and Ibn `Umar were considered too young (to take part) in the battle of Badr, and the number of the Emigrant warriors were over sixty (men) and the Ansar were over 249.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنِي مَحْمُودٌ، حَدَّثَنَا وَهْبٌ، عَنْ شُعْبَةَ، عَنْ أَبِي إِسْحَاقَ، عَنِ الْبَرَاءِ، قَالَ اسْتُصْغِرْتُ أَنَا وَابْنُ عُمَرَ يَوْمَ بَدْرٍ، وَكَانَ الْمُهَاجِرُونَ يَوْمَ بَدْرٍ نَيِّفًا عَلَى سِتِّينَ، وَالأَنْصَارُ نَيِّفًا وَأَرْبَعِينَ وَمِائَتَيْنِ.
sunnah.com