Is the son obligated to give the foster daughter a share of the inheritance he received from his father, based on a "Tanzeel" document signed by the father and two witnesses forty years before his death, which states that the foster daughter is in the status of a biological daughter and inherits like her?

Fostering orphans is one of the greatest acts of closeness to Allah. The Prophet, peace and blessings be upon him, said: "I and the guardian of the orphan will be in Paradise like this," and he pointed with his index and middle fingers. The aforementioned document is considered a valid will for the girl to be formally documented and not inherited, and the amount of the will should not exceed one-third of the estate, based on the Prophet's saying, "One-third, and one-third is much." Therefore, the father must pay what the grandfather willed, as long as it does not exceed one-third, bearing in mind that matters of inheritance are serious and complex, and a mere fatwa (definition) is not sufficient; rather, it must be referred to the Sharia (definition) courts for investigation and to guarantee the rights of heirs and creditors.