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 having his will written down regarding it.
أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ مَا حَقُّ امْرِئٍ مُسْلِمٍ لَهُ شَىْءٌ يُرِيدُ أَنْ يُوصِيَ فِيهِ يَبِيتُ لَيْلَتَيْنِ إِلاَّ وَوَصِيَّتُهُ مَكْتُوبَةٌ عِنْدَهُ