من لا يحضره الفقيه, volume 4, page 197

Hadith.5452 - Muhammad ibn Abi Umayr narrated from Abi Al-Maghra from Abu Baṣir from Abu Abdullah Imam Jafar ibn Muhammad Al-Sadiq (as), who said: "If a boy reaches the age of ten and makes a will for one-third of his wealth in a rightful cause, his will is valid. And if he is seven years old and makes a will for a small amount of his wealth in a rightful cause, his will is also valid."

Translation: Bab Ul Qaim Publications·Thaqalayn link·The Arabic above is the original.

Hadith.5453 - Ali ibn Al-Hakam narrated from Dawud ibn Al-Nuʿman from Abu Ayyub from Muhammad ibn Muslim, who said: I heard Abu Abdullah (as) say: "If a boy is on his deathbed and makes a will before reaching maturity, his will is valid if it is for his close relatives, but it is not valid for strangers."

Translation: Bab Ul Qaim Publications·Thaqalayn link·The Arabic above is the original.

Hadith.5454 - Abd Al-Ṣamad ibn Muhammad narrated from Hanan ibn Sadir from his father, from Abu Ja'far Imam Muhammad ibn Ali Al-Baqir (as), who said: "I entered upon Muhammad ibn Ali ibn Al-Hanafiyya, and his tongue had become paralyzed. I instructed him to make his will, but he did not respond. So, I ordered a basin to be brought and filled it with sand. I said to him, 'Write with your hand,' and he wrote his will in the sand with his hand, and I copied it onto a scroll."

Translation: Bab Ul Qaim Publications·Thaqalayn link·The Arabic above is the original.