It is not proper for a Muslim who has got something to bequeathe to spend even three nights without having his will written down with him regarding it. 'Abdullah b. 'Umar (Allah be pleased with them) said: Ever since I heard Messenger of Allah ﷺ say this I have not spent a night without having my will (written) along with me.
أَنَّهُ سَمِعَ رَسُولَ اللَّهِ ﷺ قَالَ مَا حَقُّ امْرِئٍ مُسْلِمٍ لَهُ شَىْءٌ يُوصِي فِيهِ يَبِيتُ ثَلاَثَ لَيَالٍ إِلاَّ وَوَصِيَّتُهُ عِنْدَهُ مَكْتُوبَةٌ قَالَ عَبْدُ اللَّهِ بْنُ عُمَرَ مَا مَرَّتْ عَلَىَّ لَيْلَةٌ مُنْذُ سَمِعْتُ رَسُولَ اللَّهِ ﷺ قَالَ ذَلِكَ إِلاَّ وَعِنْدِي وَصِيَّتِي