No personal representative shall be chargeable upon any special promise to answer damages, or to pay the debts of the testator or intestate out of his or her own estate, unless the agreement for that purpose, or some memorandum or note thereof, is in writing and signed by such personal representative, or by some other person by him or her thereunto specially authorized.
RCW 11.48.040
Agreement to answer damages from own estate must be in writing: RCW 19.36.010.