Mishkat al-Masabih 3071
Sa‘d b. Abu Waqqas said :
During an illness which brought me near to death in the year of the Conquest God’s Messenger came to visit me and I said, “Messenger of God, I have a large amount of property and my daughter is my only heir. Shall I will away all my property ?” He replied, ‘No” I suggested two-thirds, but he objected, then a half, but he still objected. When I suggested a third he replied, “You may will away a third, but that is a lot*. To leave your heirs rich is better than to leave them poor and begging from people. You will not spend anything, seeking thereby to please God, without being rewarded for it, even the mouthful you give your wife.” 

*While this tradition tells that the Prophet gave permission for a man to will away a third of his estate to some person or purpose other than the heirs, it indicates that be thought it would be better not to will away so much.

(Bukhari and Muslim.)
وَعَنْ سَعْدِ بْنِ أَبِي وَقَّاصٍ قَالَ: مَرِضْتُ عَامَ الْفَتْحِ مَرَضًا أَشْفَيْتُ عَلَى الْمَوْتِ فَأَتَانِي رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَعُودُنِي فَقُلْتُ: يَا رَسُولَ اللَّهِ: إِنَّ لِي مَالًا كَثِيرًا وَلَيْسَ يَرِثُنِي إِلَّا ابْنَتِي أَفَأُوصِي بِمَالِي كُلِّهِ؟ قَالَ: «لَا» قُلْتُ: فَثُلُثَيْ مَالِي؟ قَالَ: «لَا» قُلْتُ: فَالشَّطْرِ؟ قَالَ: «لَا» قُلْتُ: فَالثُّلُثِ؟ قَالَ: «الثُّلُثُ وَالثُّلُثُ كَثِيرٌ إِنَّكَ إِنْ تَذَرْ وَرَثَتَكَ أَغْنِيَاءَ خَيْرٌ مِنْ أَنْ تَذَرَهُمْ عَالَةً يَتَكَفَّفُونَ النَّاسَ وَإِنَّكَ لَنْ تُنْفِقَ نَفَقَةً تَبْتَغِي بِهَا وَجْهَ اللَّهِ إِلَّا أُجِرْتَ بِهَا حَتَّى اللُّقْمَةَ تَرْفَعُهَا إِلَى فِي امْرَأَتِكَ»