Sahih Bukhari Volume 7, Book 67, Hadith 5239

حَدَّثَنَا فَرْوَةُ بْنُ أَبِي الْمَغْرَاءِ، حَدَّثَنَا عَلِيُّ بْنُ مُسْهِرٍ، عَنْ هِشَامٍ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، قَالَتْ خَرَجَتْ سَوْدَةُ بِنْتُ زَمْعَةَ لَيْلاً فَرَآهَا عُمَرُ فَعَرَفَهَا فَقَالَ إِنَّكِ وَاللَّهِ يَا سَوْدَةُ مَا تَخْفَيْنَ عَلَيْنَا، فَرَجَعَتْ إِلَى النَّبِيِّ صلى الله عليه وسلم فَذَكَرَتْ ذَلِكَ لَهُ، وَهْوَ فِي حُجْرَتِي يَتَعَشَّى، وَإِنَّ فِي يَدِهِ لَعَرْقًا، فَأُنْزِلَ عَلَيْهِ فَرُفِعَ عَنْهُ وَهُوَ يَقُولُ ‏"‏ قَدْ أَذِنَ لَكُنَّ أَنْ تَخْرُجْنَ لِحَوَائِجِكُنَّ ‏"‏‏

Narrated By 'Aisha : Once Sada bint Zam'a went out at night for some need, and 'Umar saw her, and recognizing her, he said (to her), "By Allah, O Sada! You cannot hide yourself from us." So she returned to the Prophet and mentioned that to him while he was sitting in my dwelling taking his supper and holding a bone covered with meat in his hand. Then the Divine Inspiration was revealed to him and when that state was over, he (the Prophet was saying: "O women! You have been allowed by Allah to go out for your needs."