Musannaf Ibn Abi Shayba 36:188

'Abd al-Rahim narrated to us, from Ash'ath, from Ibn Sirin, from 'Ubaydah, who said: The number of those who witnessed Badr with the Prophet, may Allah bless him and grant him peace, is like the number of those who crossed the river with Talut. Their number is three hundred and thirteen.