Musnad Ahmad 30:918

'Abd al-Rahman narrated to us, 'Abd Allah ibn 'Umar narrated to us, from Sa'id ibn Abi Sa'id, from Abu Hurayrah, that Thumamah ibn Uthal (or Uthalah) accepted Islam. The Messenger of Allah (peace and blessings of Allah be upon him) said: "Take him to the garden of the sons of so-and-so, and command him to perform ghusl (a ritual bath)."