Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi)

Bukhari :: Book 5 :: Volume 59 :: Hadith 296

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.