مُوَطَّأُ مَالِكٍ
Muwatta Malik 131
Purity
حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ عَائِشَةَ، زَوْجَ النَّبِيِّ صلى الله عليه وسلم قَالَتْ فِي الْمَرْأَةِ الْحَامِلِ تَرَى الدَّمَ أَنَّهَا تَدَعُ الصَّلاَةَ .
Yahya related to me from Malik that he had heard that A'isha, the wife of the Prophet, (ﷺ), said that a pregnant woman who noticed bleeding left off from prayer.
Arabic/English book reference: Book 2, Hadith 102