Abdullah bin Umar reported,
Umar bin Khattab 
reported that he had assigned four thousand to each of the early Emigrants, distributed in four installments, but he assigned three thousand five hundred to Ibn Umar.It was said to him, "He is one of the Emigrants, so why have you given him less than four thousand?"He replied, "His parents emigrated with him. He is not like one who emigrated on his own."
Azami 8130
Sahihعن ابن عمر
عن عمر بن الخطاب رضي الله عنه، قال: كان فرض للمهاجرين الأولين أربعة آلاف في أربعة، وفرض لابن عمر ثلاثة آلاف وخمس مائة، فقيل له: هو من المهاجرين فلم نقصته من أربعة آلاف، فقال: إنما هاجر به أبواه، يقول: ليس هو كمن هاجر بنفسه.
Bukhari narrated it in the chapter on Merits (3912), from Ibrahim bin Musa, who said, Hisham (Ibn Yusuf al-Sanani) informed us, from Ibn Jurayj, who said, Ubaydullah bin Umar informed me, from Nafi, that is, from Ibn Umar, from Umar bin Khattab, and he mentioned it.