(6) باب عِدَّةِ أَصْحَابِ بَدْرٍ
Narrated Al-Bara:
We, the Companions of Muhammad used to say that the number of the warriors of Badr was the same as the number of Saul's companions who crossed the river (of Jordan) with him, and none crossed the river with him but a believer, and the were over three-hundred-and-ten men.
Reference: Sahih al-Bukhari 3958
In-book reference: Book 64, Hadith 10
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 5, Book 59, Hadith 294