(64) Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi)
كتاب المغازى
(8) Chapter: The killing of Abu Jahl
(8) باب قَتْلِ أَبِي جَهْلٍ
Sahih al-Bukhari 3970 

Narrated Abu 'Is-haq:

A man asked Al-Bara' and I was listening, "Did `Ali take part in (the battle of) Badr?" Al-Bara' said, "(Yes). he even met (his enemies) in a duel and was clad in two armors (one over the other).

حَدَّثَنِي أَحْمَدُ بْنُ سَعِيدٍ أَبُو عَبْدِ اللَّهِ، حَدَّثَنَا إِسْحَاقُ بْنُ مَنْصُورٍ، حَدَّثَنَا إِبْرَاهِيمُ بْنُ يُوسُفَ، عَنْ أَبِيهِ، عَنْ أَبِي إِسْحَاقَ، سَأَلَ رَجُلٌ الْبَرَاءَ وَأَنَا أَسْمَعُ، قَالَ أَشَهِدَ عَلِيٌّ بَدْرًا قَالَ بَارَزَ وَظَاهَرَ‏.‏
Reference : Sahih al-Bukhari 3970
In-book reference : Book 64, Hadith 23
USC-MSA web (English) reference : Vol. 5, Book 59, Hadith 309
  (deprecated numbering scheme)