'Abdullah bin 'Umar (May Allah be pleased with them) reported:
Messenger of Allah ﷺ said, "It is the duty of a Muslim who has something which is to be given as a bequest not to have it for two nights without executing a written will."

[Al-Bukhari and Muslim].

In the narration of Muslim it is narrated as 'three nights'. Ibn 'Umar (May Allah be pleased with them) said: Since I heard the Messenger of Allah say this, I have never spent a night without having my will with me.

وعنه أن رسول الله ﷺ قال: “ ما حق امرئ مسلم ، له شئ يوصي فيه ، يبيت ليلتين إلا ووصيته مكتوبة عنده” ((متفق عليه)) هذا لفظ البخاري.
وفى رواية لمسلم” يبيت ثلاث ليال: قال ابن عمر: ما مرت على ليلة منذ سمعت رسول الله ﷺ قال ذلك إلا وعندي وصيتي.