Maliks Muwatta Book 14, Hadith Number 14.
Section : Concerning Women Going Out to the Mosque.
Yahya related to me from Malik from Yahya ibn Said that Atika bint Zayd ibn Amr ibn Nufayl, the wife of Umar ibn al-Khattab, used to ask Umar ibn al-Khattab for permission to go to the mosque. He would keep silent, so she would say, “By Allah, I will go out, unless you forbid me,” and he would not forbid her.