Musnad Ahmad 658:199

Waki’ narrated to us, Isra’il narrated to us, from Abu Ishaq, from Al-Bara’ who said: The Prophet, peace and blessings of Allah be upon him, was at Al-Hudaybiyah, and Al-Hudaybiyah is a well. He said: And we were fourteen hundred. He said: So the water was scarce. He said: "He drew a bucket, then rinsed his mouth, then spat into it, and supplicated." He said: So we drank our fill, and we watered [our animals] until they were satisfied.