Sayyiduna Tamim al-Dari (may Allah be pleased with him) says: I asked the Messenger of Allah (peace and blessings be upon him) about a man who was a disbeliever and then accepts Islam at the hands of a Muslim man: what is the practice concerning him? He (peace and blessings be upon him) said: "He has the greater right over him, in his life and in his death."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الولاء / 21455