It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that Thumamah al-Hanafi was taken captive. The Prophet (peace and blessings be upon him) would go to him and say: "O Thumamah! What do you have (to say)?" He would say: If you kill, you will kill someone whose blood will be avenged; if you show favour, you will show favour to one who is grateful; and if you want wealth, we will give you whatever you wish. The Companions (may Allah be pleased with them) preferred a ransom and used to say: What will we gain by killing him? One day the Prophet (peace and blessings be upon him) passed by him and he accepted Islam. He (peace and blessings be upon him) untied him, sent him to the garden of Abu Talhah, and ordered him to take a ritual bath. He took a ritual bath and prayed two rak'ahs. The Prophet (peace and blessings be upon him) said: "Your brother's Islam is excellent."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 805
Sa'id bin Abi Sa'id al-Maqburi heard Sayyiduna Abu Hurayrah (may Allah be pleased with him) say that the Messenger of Allah (peace and blessings be upon him) sent a cavalry detachment towards Najd, and they brought back a man from the tribe of Banu Hanifah called Thumamah bin Uthal, the chief of Yamamah. The Companions tied him to one of the pillars of the mosque. In this hadith it is stated that the Messenger of Allah (peace and blessings be upon him) said: "Release Thumamah." So he went to a date-palm near the mosque, took a ritual bath, then entered the mosque and said: 'Ashhadu an la ilaha illallah wa anna Muhammadan rasulullah' (I bear witness that there is no god worthy of worship except Allah, and that Muhammad (peace and blessings be upon him) is the Messenger of Allah). And he mentioned the rest of the hadith.
(b) In Sahih al-Bukhari it is stated that the bath came before the testimony of faith. It is also possible that he accepted Islam in the presence of the Prophet (peace and blessings be upon him), then took a ritual bath, entered the mosque and declared the testimony openly; this reconciles the two narrations.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 806
Sayyiduna Qays bin Asim (may Allah be pleased with him) came to the Prophet (peace and blessings be upon him) and accepted Islam, and the Prophet (peace and blessings be upon him) ordered him "to take a ritual bath with water and lote-tree leaves."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 807
Qays bin Asim (may Allah be pleased with him) came to the Prophet (peace and blessings be upon him) intending to accept Islam, and the Prophet (peace and blessings be upon him) ordered him "to take a ritual bath with water and lote-tree leaves." (b) Muhammad bin Kathir and a group narrated it with the same meaning; most of them say that it is narrated from his grandfather, Qays bin Asim (may Allah be pleased with him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 808
Qays bin Asim (may Allah be pleased with him) came to the Prophet (peace and blessings be upon him), and the Prophet (peace and blessings be upon him) ordered him "to take a ritual bath with water and lote-tree leaves."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 809
Uthaym bin Kulayb narrates from his father, who narrates from his grandfather (may Allah be pleased with him), that he came to the Prophet (peace and blessings be upon him) and said: I have become a Muslim. The Prophet (peace and blessings be upon him) said to him: "Cast off from yourself the hair of disbelief." (He meant: shave your head.) The narrator says: Another narrator informed me that the Prophet (peace and blessings be upon him) said to another man who was with him: "Cast off from yourself the hair of disbelief, and get circumcised."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 811