Musnad Ahmad 26:811

Hashim ibn al-Qasim narrated to us, al-Mas'udi narrated to us, from Abu Nahshal, from Abu Wa'il, who said: 'Abdullah said: The people favored 'Umar ibn al-Khattab, may Allah be pleased with him, for four things: For his mention of the captives on the day of Badr; he ordered their killing, so Allah, the Almighty and Majestic, revealed: "Had it not been for a decree from Allah that preceded, you would have been touched by a great punishment for what you took." [Al-Anfal: 68]. And for his mention of the hijab; he ordered the wives of the Prophet, may Allah bless him and grant him peace, to observe the hijab. Zaynab said to him: "Are you [admonishing] us, O son of al-Khattab, while the revelation descends in our houses?" So Allah, the Almighty and Majestic, revealed: "And when you ask them for something, ask them from behind a partition." [Al-Ahzab: 53]. And for the supplication of the Prophet, may Allah bless him and grant him peace, for him: "O Allah, strengthen Islam with 'Umar." And for his opinion regarding Abu Bakr; he was the first of the people to pledge allegiance to him.