Riyad as-Salihin, Book 1, Hadith 595 (In-Book) ⓘ

Nafi' (May Allah be pleased with him) reported: 'Umar bin Al-Khattab (May Allah be pleased with him) fixed the payment amounting to four thousand dirhams for each of the early Emigrants, but for his son, he fixed only three thousand five hundred. He was asked: "He is also an (early) Emigrant, why have you fixed a lesser sum for him?" He said: "It was his father who took him along with him. He is not like one who emigrated by himself."[Al-Bukhari].

وعن نافع أن عمر بن الخطاب رضي الله عنه كان فرض للمهاجرين الأولين أربعة آلاف وفرض لابنه ثلاثة آلاف وخمسمائة، فقيل له‏:‏ هو من المهاجرين فلم نقصته‏؟‏ فقال‏:‏ إنما هاجر به أبوه، يقول‏:‏ ليس هو كمن هاجر بنفسه” ‏(‏‏(‏رواه البخاري‏)‏‏)‏