Narrated Ibn 'Umar (RA):

Allah's Messenger (ﷺ) said: "It is not permissible for a Muslim person, who has something he wants to give as a bequest, to have it for two nights without having his will regarding it written and kept ready with him." [Agreed upon].

عَنْ اِبْنِ عُمَرَ ‏- رَضِيَ اَللَّهُ عَنْهُمَا‏- ; أَنَّ رَسُولَ اَللَّهِ ‏- صلى الله عليه وسلم ‏-قَالَ : { مَا حَقُّ اِمْرِئٍ مُسْلِمٍ لَهُ شَيْءٌ يُرِيدُ أَنْ يُوصِيَ فِيهِ يَبِيتُ لَيْلَتَيْنِ إِلَّا وَوَصِيَّتُهُ مَكْتُوبَةٌ عِنْدَهُ } مُتَّفَقٌ عَلَيْهِ [1]‏ .‏