He embraced Islam, and the Prophet ﷺ instructed him to perform a full bath with water and lote-tree leaves.
أخبرنا عمرو بن علي قال حدثنا يحيى قال حدثنا سفيان عن الأغر وهو ابن الصباح عن خليفة بن حصين
أنه أسلم فأمره النبي ﷺ أن يغتسل بماء وسدر
Sourcing, sahih. Reported by Abu Dawud, Purification, chapter on the man who accepts Islam and is ordered to perform ghusl, no. 355, and Tirmidhi, Friday Prayer, chapter on what is mentioned regarding ghusl when a man accepts Islam, no. 605, from the hadith of Sufyan Thawri, through the same chain. Tirmidhi said, hasan. Ibn Khuzayma graded it sahih, no. 254, 255, as did Ibn Hibban, no. 234, and Ibn Jarud, no. 14, and others. It also appears in Kubra, no. 193, and it has corroborating narrations in Bukhari, Muslim, and others.