Musnad Ahmad 1153:1848

Hajjaj narrated to us, he said: Layth narrated to us, he said: Uqayl narrated to me, from Ibn Shihab, from Urwah ibn al-Zubayr, from Aisha, that the wives of the Prophet, peace and blessings of Allah be upon him, used to go out at night when they needed to relieve themselves to the *Manasi’*, which is a spacious open ground. Umar ibn al-Khattab used to say to the Messenger of Allah, peace and blessings of Allah be upon him: "Veil your women." But the Messenger of Allah, peace and blessings of Allah be upon him, did not do so. Then Sawdah bint Zam'ah, the wife of the Prophet, peace and blessings of Allah be upon him, went out one night during the time of *Isha*, and she was a tall woman. Umar called out to her: "Indeed, we have recognized you, O Sawdah," out of his eagerness for the revelation of the verse of the veil. Aisha said: Then the verse of the veil was revealed.