Sahih Bukhari | Volume 7 | Hadith Number 164
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."