مُوَطَّأُ مَالِكٍ
Muwatta Malik 137
Purity
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ زَيْنَبَ بِنْتِ أَبِي سَلَمَةَ، أَنَّهَا رَأَتْ زَيْنَبَ بِنْتَ جَحْشٍ الَّتِي كَانَتْ تَحْتَ عَبْدِ الرَّحْمَنِ بْنِ عَوْفٍ وَكَانَتْ تُسْتَحَاضُ فَكَانَتْ تَغْتَسِلُ وَتُصَلِّي .
Yahya related to me from Malik from Hisham ibn Urwa from his father from Zaynab bint Abu Salama that she saw Zaynab bint Jahsh, the wife of Abd ar-Rahman ibn Awf, and she used to bleed as if menstruating. She would do ghusl and pray.
Arabic/English book reference: Book 2, Hadith 108