It is narrated from Sayyiduna Abdullah bin Umar, may Allah be pleased with him, that the Messenger of Allah, peace and blessings be upon him, said: "It is not proper for a person who considers the will to be a right and has property worthy of bequest, to spend even two nights without having his will written with him."
Hadith Referenceالسنن المأثورة / باب ما جاء في فدية الأذى / 511
Hadith Takhrijسنن ترمذی، الوصايا، باب ماجاء في الحث على الوصية، رقم: 2118 حسن صحيح، وقال الالبانی: صحيح، مسند احمد: 184/8، رقم: 4578 وقال الارنوؤط: حديث صحيح