The Book of Wills
30/1. Chapter:
It Is Disliked To Delay Making A Will
Sunan an-Nasai
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 ".
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.'"
Reference : Sunan an-Nasa'i 3615In-book reference : Book 30, Hadith 5English translation : Vol. 4, Book 30, Hadith 3645