Al-Kāfi - Volume 7 > The Matters for which one can Make a Will and what is Preferable in the Issue
Hadith #7

7- عَلِيُّ بْنُ إِبْرَاهِيمَ عَنْ أَبِيهِ عَنِ النَّوْفَلِيِّ عَنِ السَّكُونِيِّ عَنْ أَبِي عَبْدِ اللهِ (عَلَيْهِ السَّلام) قَالَ قَالَ أَمِيرُ الْمُؤْمِنِينَ (عَلَيْهِ السَّلام) مَنْ أَوْصَى بِثُلُثِ مَالِهِ ثُمَّ قُتِلَ خَطَأً فَإِنَّ ثُلُثَ دِيَتِهِ دَاخِلٌ فِي وَصِيَّتِهِ.

7. Ali ibn Ibrahim has narrated from his father from al-Nawfaliy from al-Sakuniy who has narrated the following: “Abu ‘Abd Allah, ‘Alayhi al-Salam, has said that ’Amir al-Mu’minin has said, ‘If one makes a will about one-third of his legacy, then is killed by mistake, one-third of the wergild for him becomes part of that which he has willed.’”