What is the ruling of Islamic law regarding a son disclosing, after his father's death, that his father had written for him an entitlement to one feddan out of two, and how is the inheritance to be distributed in this case?

As long as the son did not take possession of the feddan and did not acquire it until the father died, it becomes an inheritance to be distributed among all heirs; based on the hadith of Aisha, may Allah be pleased with her, that Abu Bakr, may Allah be pleased with him, gifted her twenty wasqs of harvested dates. When he fell ill, he said: "O my daughter, I had gifted you twenty wasqs of harvested dates. If you had acquired it or taken possession of it, it would have been yours. But today it is inherited property, so divide it according to the Book of Allah." And according to the jurists' saying: "If the donor or the donee dies before possession, the gift becomes void."

Therefore, all that the father left behind is to be distributed among his heirs, including the two agricultural feddans: the wife receives one-eighth, and the remainder is divided among the three daughters and the son, with the male receiving the share of two females.