Musannaf Ibn Abi Shayba 9:468

Hafs narrated to us, from Ash'ath and Hisham, from Ibn Sirin, from Abu al-Ajfa' al-Sulami, from Umar, who said: "Do not be excessive in the dowries of women, for if it were an honor in this world or a piety before Allah, Muhammad would have been more entitled to it than you, and more worthy of it. He did not marry any of his daughters, nor did he marry any of his wives, for more than twelve uqiyah."