It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "It is not right for a Muslim man who has wealth about which a will is made to spend even a single night of his time without his will being written and present with him."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13132