Mus'ab b. Sa'd reported on the authority of his father. I was ailing. I sent message to Allah's Apostle ﷺ saying: Permit me to give away my property as I like. He refused. I (again) said: (Permit me) to give away half. He (again refused). I (again said): Then one-third. He (the Holy Prophet) observed silence after (I had asked permission to give away) one-third. He (the narrater) said: It was then that endowment of one-third became permissible.

وَحَدَّثَنِي زُهَيْرُ بْنُ حَرْبٍ، حَدَّثَنَا الْحَسَنُ بْنُ مُوسَى، حَدَّثَنَا زُهَيْرٌ، حَدَّثَنَا سِمَاكُ، بْنُ حَرْبٍ حَدَّثَنِي مُصْعَبُ بْنُ سَعْدٍ، عَنْ أَبِيهِ، قَالَ مَرِضْتُ فَأَرْسَلْتُ إِلَى النَّبِيِّ ﷺ فَقُلْتُ دَعْنِي أَقْسِمْ مَالِي حَيْثُ شِئْتُ فَأَبَى . قُلْتُ فَالنِّصْفُ فَأَبَى . قُلْتُ فَالثُّلُثُ قَالَ فَسَكَتَ بَعْدَ الثُّلُثِ . قَالَ فَكَانَ بَعْدُ الثُّلُثُ جَائِزًا .