The Statement of Allah the Most High: "...When they gave their Bai'a (pledge) to you (O Muḥammad pbuh) under the tree..." (V.48:18) Sahih al-Bukhari 4840
Arabic hadith text
حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا سُفْيَانُ، عَنْ عَمْرٍو، عَنْ جَابِرٍ، قَالَكُنَّا يَوْمَ الْحُدَيْبِيَةِ أَلْفًا وَأَرْبَعَمِائَةٍ.
Translation
Narrated Jabir
We were one thousand and four hundred on the Day of Al-Hudaibiya.