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 who has wealth and wishes to make a bequest from it to spend one night or two nights without having written his bequest."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الوصايا / 12589