Musnad Ahmad 333:36

Yahya ibn Sa'id narrated to us, from Yazid ibn Abi 'Ubayd, who said: Salamah ibn al-Akwa' narrated to me, saying: The Messenger of Allah (may Allah bless him and grant him peace) went out to some people from Aslam while they were competing in archery in the market. He said: "Shoot, O sons of Ishmael, for your father was an archer. Shoot, and I am with the sons of so-and-so," for one of the two groups. They held back their hands. He said: "Shoot." They said: "O Messenger of Allah, how shall we shoot while you are with the sons of so-and-so?" He said: "Shoot, and I am with all of you."