Sahih Bukhari
Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi)
Volume: 005 / Book Number: 059 / Hadith Number: 293
Narrated Al-Bara:
The companions of (the Prophet) Muhammad who took part in Badr, told me that their number was that of Saul's (i.e. Talut's) companions who crossed the river (of Jordan) with him and they were over three-hundred-and-ten men. By Allah, none crossed the river with him but a believer. (See Qur'an 2:249)