Sawda went out after the verse of hijab had been revealed, to attend to a need of hers. She was a large woman who could not be missed by anyone who knew her. Umar bin Khattab saw her and said, "Sawda, by Allah, you are not hidden from us. So consider how you go out."
خرجت سودة بعدما ضرب الحجاب الحاجتها، وكانت امرأة جسيمة لا تخفى على من يعرفها، فرآها عمر بن الخطاب فقال: يا سودة، أما والله ما تخفين علينا، فانظري كيف تخرجين.
Bukhari related it in the Book of Tafsir (4795), and Muslim in the Book of Greetings (2170), both from the hadith of Abu Usama, from Hisham, from his father, from Ayesha, and he mentioned it.His statement, "would not be hidden from one who knew her," means because of the size of her body, not because of her face.