Is it Islamically permissible to execute a waiver by a father, while on his deathbed, of a plot of land to one of his daughters under pressure from her husband, where the husband claimed the existence of signatures from the two brothers but not the fourth sister and the mother, while the rest of the heirs are unaware of this waiver?

"Muzara'a (sharecropping) is a contract that does not transfer ownership of the land to the laborer. It becomes void upon the death of either party according to the Hanafis and Hanbalis. The father's relinquishment of his share of the produce during his death illness is considered a bequest and is not permissible for an heir. Such relinquishment is not established except with clear evidence. Disputes of this nature should be referred to the Sharia court."