Musannaf Ibn Abi Shayba 1:527

Ali ibn Mushir narrated to us, from Yahya ibn Sa'id, from Bashir ibn Yasar, who said: Suwayd ibn al-Nu'man al-Ansari informed me that they went out with the Messenger of Allah, may Allah bless him and grant him peace, to Khaybar. When they were at al-Sahba', he prayed the Asr prayer. Then he called for food, and nothing was brought to him except parched barley (sawiq), so they ate and drank. Then he called for water and rinsed his mouth, then he stood up and led us in the Maghrib prayer.