Rabi'ah said:

Umm Habibah daughter of Jahsh had a prolonged flow of blood. The Prophet (ﷺ) commander her to refrain (from prayer) during her menstrual period; then she should wash and pray. If she sees anything (which renders ablution void) she should perform ablution and pray. Abu Dawud said: This is the view held by Malik b. Anas.

حَدَّثَنَا عَبْدُ الْمَلِكِ بْنُ شُعَيْبٍ، حَدَّثَنِي عَبْدُ اللَّهِ بْنُ وَهْبٍ، أَخْبَرَنَا اللَّيْثُ، عَنْ رَبِيعَةَ، أَنَّهُ كَانَ لاَ يَرَى عَلَى الْمُسْتَحَاضَةِ وُضُوءًا عِنْدَ كُلِّ صَلاَةٍ إِلاَّ أَنْ يُصِيبَهَا حَدَثٌ غَيْرُ الدَّمِ فَتَوَضَّأُ ‏.‏ قَالَ أَبُو دَاوُدَ هَذَا قَوْلُ مَالِكٍ يَعْنِي ابْنَ أَنَسٍ ‏.‏