Musnad Ahmad 176:1

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from Yahya ibn Sa‘id, who said: I heard Bashir ibn Yasar, who said: I heard Suwayd ibn al-Nu‘man, a man from the companions of the Messenger of Allah (may Allah bless him and grant him peace), from the companions of the Tree, say: "The Messenger of Allah (may Allah bless him and grant him peace) was on a journey, and they had no food. He said: So they were brought some parched barley (sawiq), and they chewed on it and drank from it. Then they were brought water, and they rinsed their mouths. Then the Messenger of Allah (may Allah bless him and grant him peace) stood up and prayed."