As regards your question, the late Sheikh Ibn Baz, a prominent and well-known Muslim scholar, stated,

Wasiyyah (will) is not obligatory but it is recommendable if a Muslim wishes to make a will as regards something. It should not exceed the third of a person’s properties and the testator should clarify in his wasiyyah the legal ways where his or her will be spent and the trustee of his or her wasiyyah.

It is authentically reported by Al-Bukhari and Muslim on the authority of Ibn `Umar (may Allah be pleased with him) that the Prophet (peace be upon him) said, “It is not permissible for any Muslim who has something to will in it, to stay for two nights without having his last will kept ready with him.

If a person is committed to undocumented debts or rights, he or she is obliged to put a wasiyyah as regarding them. Moreover, two trustworthy persons should witness the wasiyyah and it is advisable to write it by a qualified and reliable scholar. May Allah grant all of us all success!”