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)
Hadith Referenceصحيح البخاري / كتاب المغازي / 3957
Hadith Gradingمحدثین:أحاديث صحيح البخاريّ كلّها صحيحة
Hadith Commentary: The faithless ones, having drunk the water of the river impatiently and excessively, had swollen their bellies and lost their strength.
Source: Sahih Bukhari: Commentary by Maulana Dawood Raz, Page: 3957
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.