Musnad Abu Ya'la al-Mawsili 6:58

Ibn Numayr narrated to us, Ibn Fudayl narrated to us, from ‘Ata’ ibn al-Sa’ib, from Abu ‘Abd al-Rahman, who said: Sa’d ibn Abi Waqqas said regarding the age of one-third: I became ill with an illness, and the Messenger of Allah (may Allah bless him and grant him peace) visited me during it. He said: "Have you made a will?" I said: "I have made a will for all of my wealth." He said: "Then what have you left for your heirs?" I said: "They are wealthy." He said: "Make a will for one-tenth, and leave the rest of it for your heirs," and he mentioned the rest of the hadith.