Is it permissible for me to refuse to sign a contract with my father to give him a third of my salary after marriage, knowing that I already give him a large portion of my salary now, and I fear his anger and his prayers against me due to accumulated debts?

It is not permissible for a father to take a portion of his son's salary, nor is the son obliged to agree to this condition, especially if it causes him harm. The permissibility of a parent taking from his child's wealth is restricted by conditions. The supplication of a parent against his child is likely to be answered; therefore, the father should be reminded to fear Allah and not to supplicate against his son. The son, for his part, should honor his father and give him some money to avert his anger and supplication, seeking reward from Allah.