حَدَّثَنَا مُسَدَّدُ بْنُ مُسَرْهَدٍ، حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، عَنْ عُبَيْدِ اللَّهِ، حَدَّثَنِي نَافِعٌ، عَنْ عَبْدِ اللَّهِ، - يَعْنِي ابْنَ عُمَرَ - عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم قَالَ ‏"‏ مَا حَقُّ امْرِئٍ مُسْلِمٍ لَهُ شَىْءٌ يُوصِي فِيهِ يَبِيتُ لَيْلَتَيْنِ إِلاَّ وَوَصِيَّتُهُ مَكْتُوبَةٌ عِنْدَهُ ‏"‏ ‏.‏

Narrated 'Abdullah bin 'Umar: The Messenger of Allah (PBUH) as saying: It is the duty of a Muslim man who has something which is to be given as bequest not to have it for two nights without having his will written regarding it. Translation Not Available

Book Ref: Sunan Abi Dawud Book 18 Hadith 2862
Web Ref:  Sunan Abi Dawud Book 17 Hadith 2856