Sahih Muslim Book: 26, Hadith: 4294

حَدَّثَنَا هَارُونُ بْنُ مَعْرُوفٍ، حَدَّثَنَا عَبْدُ اللَّهِ بْنُ وَهْبٍ، أَخْبَرَنِي عَمْرٌو، – وَهْوَ ابْنُ الْحَارِثِ – عَنِ ابْنِ شِهَابٍ، عَنْ سَالِمٍ، عَنْ أَبِيهِ، أَنَّهُ سَمِعَ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏ “‏ مَا حَقُّ امْرِئٍ مُسْلِمٍ لَهُ شَىْءٌ يُوصِي فِيهِ يَبِيتُ ثَلاَثَ لَيَالٍ إِلاَّ وَوَصِيَّتُهُ عِنْدَهُ مَكْتُوبَةٌ ‏”‏ ‏.‏ قَالَ عَبْدُ اللَّهِ بْنُ عُمَرَ مَا مَرَّتْ عَلَىَّ لَيْلَةٌ مُنْذُ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ذَلِكَ إِلاَّ وَعِنْدِي وَصِيَّتِي ‏.‏ Salim reported on the authority of his father (‘Abdullah b. Umar) that he (his father) had heard Allah’s Messenger (may peace be upon him) 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 (may peace be upon him) say this I have not spent a night without having my will (written)