كتاب الوصية
Read the English translation first, with the original Arabic directly underneath.
Salim reported on the authority of his father ('Abdullah b. Umar) that he (his father) had heard Allah's Messenger (ﷺ) as saying:
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 Allah's Messenger (ﷺ) say this I have not spent a night without having my will (written) along with me.
مَا حَقُّ امْرِئٍ مُسْلِمٍ لَهُ شَىْءٌ يُوصِي فِيهِ يَبِيتُ ثَلاَثَ لَيَالٍ إِلاَّ وَوَصِيَّتُهُ عِنْدَهُ مَكْتُوبَةٌ