How authentic is the statement of Omar ibn al-Khattab, may Allah be pleased with him: "Since when have you enslaved people, though their mothers bore them free?" And what is its complete story and its sources?

The story mentioned in the book "Al-Wilayah ala al-Buldan" (Authority over Countries) recounts an incident that occurred when Amr ibn al-Aas was the governor of Egypt during the caliphate of Umar ibn al-Khattab. Amr ibn al-Aas's son struck a Coptic youth during a horse race. The youth's father went to Medina and complained to Umar. Umar summoned Amr ibn al-Aas and his son, and gave the Coptic youth a whip to retaliate against Amr ibn al-Aas's son. After the youth had retaliated, Umar said, "Had you struck Amr ibn al-Aas, I would not have prevented you, for the youth only struck you due to his father's authority." Then he turned to Amr ibn al-Aas, saying, "When did you enslave people, though their mothers bore them free?"