Sahih al-Bukhari 4155
Book 64: Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi)
Arabic
وَقَالَ عُبَيْدُ اللَّهِ بْنُ مُعَاذٍ حَدَّثَنَا أَبِي، حَدَّثَنَا شُعْبَةُ، عَنْ عَمْرِو بْنِ مُرَّةَ، حَدَّثَنِي عَبْدُ اللَّهِ بْنُ أَبِي أَوْفَى ـ رضى الله عنهما ـ كَانَ أَصْحَابُ الشَّجَرَةِ أَلْفًا وَثَلاَثَمِائَةٍ، وَكَانَتْ أَسْلَمُ ثُمْنَ الْمُهَاجِرِينَ. تَابَعَهُ مُحَمَّدُ بْنُ بَشَّارٍ حَدَّثَنَا أَبُو دَاوُدَ حَدَّثَنَا شُعْبَةُ.
English translation
Abdullah bin Abi `Aufa said, "The people (who gave the Pledge of allegiance) under the Tree numbered 1300 and the number of Bani Aslam was 1/8 of the Emigrants
Reference: Sahih al-Bukhari 4155, Book of Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi). English translation by Dr. Muhammad Muhsin Khan.