Musannaf Ibn Abi Shayba 28:350

Muhammad ibn Bakr narrated to us, from Ibn Jurayj, who said: Abu Bakr said—I think he mentioned an isnad for it—that Umar ibn al-Khattab allotted three thousand and five hundred to Usama ibn Zayd, and three thousand to Abdullah ibn Umar. Abdullah said to Umar: "You allotted three thousand and five hundred to Usama, yet he is not earlier than me in Islam, nor did he witness what I did not witness." He said: So Umar said: "Because Zayd ibn Harithah was more beloved to the Messenger of Allah, may Allah bless him and grant him peace, than your father, and Usama ibn Zayd was more beloved to the Messenger of Allah, may Allah bless him and grant him peace, than you. Therefore, I gave him five hundred more than you."