أَخْبَرَنَا أَحْمَدُ بْنُ يَحْيَى بْنِ الْوَزِيرِ بْنِ سُلَيْمَانَ، قَالَ سَمِعْتُ ابْنَ وَهْبٍ، قَالَ أَخْبَرَنِي يُونُسُ، وَعَمْرُو بْنُ الْحَارِثِ، عَنِ ابْنِ شِهَابٍ، عَنْ سَالِمِ بْنِ عَبْدِ اللَّهِ، عَنْ أَبِيهِ، عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم قَالَ ‏"‏ مَا حَقُّ امْرِئٍ مُسْلِمٍ لَهُ شَىْءٌ يُوصَى فِيهِ فَيَبِيتُ ثَلاَثَ لَيَالٍ إِلاَّ وَوَصِيَّتُهُ عِنْدَهُ مَكْتُوبَةٌ ‏"‏‏.‏

It was narrated from Salim bin 'Abdullah, from his father, that the Messenger of Allah said: "It is not right for a Muslim who has anything concerning which a will should be made, to abide for more than three nights without having a written will with him." Translation Not Available

Book Ref: Sunan An Nisai Book 30 Hadith 3619
Web Ref:  Sunan An Nisai Vol 4 Book 30 Hadith 3649