It is narrated from Ibn Umar (may Allah be pleased with them both) that Umar bin al-Khattab (may Allah be pleased with him) said: He allotted four thousand each for the first Muhajirun, and three thousand five hundred for Ibn Umar (may Allah be pleased with them both). It was said: He too is one of the Muhajirun, so why less than four thousand for him? He said: His parents migrated with him; he is not like one who migrated by himself.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الفيء والغنيمة / 12993