Sayyiduna Ibn Umar (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) said: "When your women ask your permission to go to the mosque, or he said: to the mosques, then give them permission."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5368