 primary sources from Muslim contemporary chroniclers also stated the inclusion of famous Usama ibn Zayd, son of Zayd ibn Haritha who fell earlier in the battle of Mu'tah.Despite relative his young age, Usama already possessed battle experience, including from the battle of Mu'tah where his father died and later fought under command of Khalid ibn Al-Walid.Aside from huge portions Medina war veterans, the prophet also enlisted some tribes who had already accepted to Islam and come to his aid in the event of great opposition.After Marching for 10 days, Amr ibn al-As encamped at a spring called Salasil, there he found that the enemy was assembled in large numbers, so he sent a messenger back to Muhammad asking for reinforcement.