Hadith 504690
Chapter 14: The Qibla - كتاب القبلة
حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، أَنَّهُ قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " لاَ تَمْنَعُوا إِمَاءَ اللَّهِ مَسَاجِدَ اللَّهِ " .
Yahya related to me from Malik that he had heard that Abdullah ibn Umar said, "The Messenger of Allah, may Allah bless him and grant him peace, said, 'Do not forbid the female slaves of Allah from (going into) the mosques of Allah.' "
Reference Muwatta Malik 504690
USC-MSA web (English) reference : Book 14, Hadith 12