Musnad Abu Ya'la al-Mawsili 2:15

'Abd al-A'la ibn Hammad al-Narsi narrated to us, Bishr ibn Mansur narrated to us, 'Ubayd Allah ibn 'Umar narrated to us, from Nafi', from Ibn 'Umar, who said: 'Umar said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Do not prevent the female servants of Allah from the mosques of Allah."