ENOfficial
It has been narrated (through a different chain of transmitters) on the authority of Salim b. al-Ja'd who said: I asked Jabir: How many were you on the Day of Hudaibiya? He said: One thousand and four hundred.
Source: sunnah.com
Other translations
Arabic
وَحَدَّثَنَا عُثْمَانُ بْنُ أَبِي شَيْبَةَ، وَإِسْحَاقُ بْنُ إِبْرَاهِيمَ، قَالَ إِسْحَاقُ أَخْبَرَنَا وَقَالَ، عُثْمَانُ حَدَّثَنَا جَرِيرٌ، عَنِ الأَعْمَشِ، حَدَّثَنِي سَالِمُ بْنُ أَبِي الْجَعْدِ، قَالَ قُلْتُ لِجَابِرٍ كَمْ كُنْتُمْ يَوْمَئِذٍ قَالَ أَلْفًا وَأَرْبَعَمِائَةٍ .
sunnah.com