Musannaf Ibn Abi Shayba 16:532

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Ibn Abi Layla, from Muhammad bin Abd al-Rahman, from Muhammad bin Sharhabil, from Qays bin Sa’d, who said: The Prophet, peace be upon him, came to us, so we placed water for him to cool himself with, and he performed ghusl. Then I brought him a yellow sheet, and I saw the trace of wars (a yellow dye) on his abdominal folds.