And the Prophet (peace be upon him) said, "A man's will should be written." And Allah the Exalted said (in Surah Al-Baqarah) «كتب عليكم إذا حضر أحدكم الموت إن ترك خيرا الوصية للوالدين والأقربين بالمعروف حقا على المتقين * فمن بدله بعد ما سمعه فإنما إثمه على الذين يبدلونه إن الله سميع عليم * فمن خاف من موص جنفا أو إثما فأصلح بينهم فلا إثم عليه إن الله غفور رحيم‏» "It is prescribed for you, when death approaches any of you and he leaves some wealth, that he should make a bequest for parents and near relatives according to what is acceptable—a duty upon the righteous. Then whoever changes it after he has heard it, the sin is only upon those who change it. Indeed, Allah is Hearing and Knowing. But if someone fears from the bequeather some error or sin and makes peace between them, there is no sin upon him. Indeed, Allah is Forgiving and Merciful." (In the Ayah) «جنفا» means to incline to one side, and «متجانف» means one who inclines.

Narrated `Abdullah bin `Umar: Allah's Apostle said, "It is not permissible for any Muslim who has something to will to stay for two nights without having his last will and testament written and kept ready with him."