Musannaf Ibn Abi Shayba 17:1020

'Abd al-Rahim ibn Sulayman narrated to us, from 'Abd Allah ibn Sa'id, from his father, from Abu Hadrad al-Aslami, who said: The Messenger of Allah passed by some people from Aslam while they were competing in archery. He said, "Shoot, O sons of Ishmael, for your father was an archer. Shoot, and I am with Ibn al-Adra'." The people held back their hands. They said, "O Messenger of Allah, shall we shoot while you have said, 'I am with Ibn al-Adra',' and we know that your party is not defeated?" He said, "Shoot, and I am with all of you."