Abdullah bin Umar reported,

Ibn Umar said, "The Messenger of Allah ﷺ reviewed me for combat on the day of Uhud, when I was fourteen years old, and he did not permit me to take part. Then he reviewed me on the day of the Trench, when I was fifteen years old, and he permitted me."Nafi said, "I came to Umar bin Abdul-Aziz, who was caliph at that time, and I related this hadith to him."Umar bin Abdul-Aziz said, "This is indeed the dividing line between a minor and an adult."He then wrote to his governors instructing them to assign a stipend to anyone who had reached fifteen years of age, and to count anyone younger than that among the dependents.In their version of the hadith, the wording is, "I was fourteen years old, and he considered me too young."

Muslim 4838

Sahih

و حدثناه أبو بكر بن أبي شيبة حدثنا عبد الله بن إدريس وعبد الرحيم بن سليمان ح و حدثنا محمد بن المثنى حدثنا عبد الوهاب يعني الثقفي جميعا عن عبيد الله بهذا الإسناد غير أن في حديثهم وأنا ابن أربع عشرة سنة فاستصغرني

مسلم 4838صحيح
Contents
Reference
Commentary
Ayat
Collection
Sahih Muslim
Book
Leadership
Chapter
Clarification of the age of maturity
Numbering
Darussalam 4838
Muslim 4838