Musnad Ahmad 658:97

Abu Ahmad narrated to us, Israel narrated to us, from Abu Ishaq, from Al-Bara’ who said: "We were with the Messenger of Allah, may Allah bless him and grant him peace, fourteen hundred [men] at Al-Hudaybiyyah. Al-Hudaybiyyah is a well, and we drew its water until we left nothing in it. That was mentioned to the Prophet, may Allah bless him and grant him peace, so he came and sat on its edge. He called for a vessel, rinsed his mouth, and then spat into it. Then we left it for a short while, and it provided us and our mounts with water, and we drank from it as much as we wished."