Musnad Ahmad 30:3138

Surayj narrated to us, he said: Abdullah—meaning Ibn Umar—narrated to us, from Sa’id al-Maqburi, from Abu Hurayrah, that Thumamah ibn Uthal al-Hanafi accepted Islam. The Prophet, peace and blessings of Allah be upon him, ordered that he be taken to the garden of Abu Talhah to perform ghusl (ritual washing). The Messenger of Allah, peace and blessings of Allah be upon him, said: "Your companion’s Islam has become excellent."