Musnad Ahmad 176:0

Suwayd ibn al-Nu‘man reported: We went out with the Messenger of Allah (may Allah bless him and grant him peace) toward Khaybar. When we reached al-Sahba’—which is at the lower end of Khaybar—he prayed the afternoon prayer (Asr). Then he called for food, and nothing was brought to him except parched barley (sawiq). He commanded it to be moistened, and he ate, and we ate with him. Then he stood up for the sunset prayer (Maghrib), rinsed his mouth with water, and we rinsed our mouths with him. Then he prayed without performing ablution.