Musannaf Ibn Abi Shayba 36:190

Waki' narrated to us, he said: Sufyan and Isra'il narrated to us, from Abu Ishaq, from al-Bara' ibn 'Azib, who said: The number of the companions of the Prophet, may Allah bless him and grant him peace, was three hundred and some odd [men]. And they used to consider that they were the number of the companions of Talut on the day of Jalut, those who crossed the river with him; and none crossed the river with him except a believer.