From Sahih Bukhari (Hadith 4153):
Narrated Qatada:I said to Sa`id bin Al-Musaiyab, "I have been informed that Jabir bin `Abdullah said that the number (of Al-Hudaibiya Muslim warriors) was 1400." Sa`id said to me, "Jabir narrated to me that they were 1500 who gave the Pledge of allegiance to the Prophet (ﷺ) on the day of Al-Hudaibiya
Reference: Bukhari 4153