Musannaf Ibn Abi Shayba 26:557

We were narrated by Abd al-A’la, from Yunus, from al-Hasan, regarding a man who formed a bond of guardianship (wala) with another man, and he (the latter) accepted Islam at his hands. He said: He does not inherit from him, except that if he wishes, he may bequeath to him all of his wealth.