Narrated Al-Bara: We used to say that the warriors of Badr were over three-hundred-and-ten, as many as the Companions of Saul who crossed the river with him; and none crossed the river with him but a believer.
— Sahih Bukhari, Volume 5, Book 59: Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi), Hadith #296