With regard to the bravery of Hazrat Sa‘d (ra) during the Battle of Badr, there is a narration that despite being on foot, Hazrat Sa‘d (ra) was fighting with the same valour as the cavaliers.
(Al-Tabaqaat-ul-Kubra li ibn Sa‘d, Vol. 3, p. 104, Sa‘d (ra) bin Abi Waqas, Dar-ul-Kutub al-Ilmiyyah, Beirut, Lebanon 1990)
This is why Hazrat Sa‘d (ra) was given the title “Faris-ul-Islam”, i.e., the Cavalier of Islam.
(Umdatul Qari Sharah Sahih Bukhari, Vol. 1, p. 305, Dar-ul-Kutub al-Ilmiyyah, Beirut, 2001)