Sunan an-Nasa'i 3615
It was narrated that Ibn 'Umar said:
"The Messenger of Allah said: 'It is not befitting for a Muslim who has anything concerning which a will should be made, to abide for two nights without having a written will with him.'"
أَخْبَرَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، قَالَ حَدَّثَنَا الْفُضَيْلُ، عَنْ عُبَيْدِ اللَّهِ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏
"‏ مَا حَقُّ امْرِئٍ مُسْلِمٍ لَهُ شَىْءٌ يُوصَى فِيهِ أَنْ يَبِيتَ لَيْلَتَيْنِ إِلاَّ وَوَصِيَّتُهُ مَكْتُوبَةٌ عِنْدَهُ ‏"‏‏.‏