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