Narrated 'Aisha:

Fatima bint Abi Hubaish came to the Prophet and said, "O Allah's Apostle I get persistent bleeding from the uterus and do not become clean. Shall I give up my prayers?" Allah's Apostle replied, "No, because it is from a blood vessel and not the menses. So when your real menses begins give up your prayers and when it has finished wash off the blood (take a bath) and offer your prayers." Hisham (the sub narrator) narrated that his father had also said, (the Prophet told her): "Perform ablution for every prayer till the time of the next period comes."

حَدَّثَنَا مُحَمَّدٌ، قَالَ حَدَّثَنَا أَبُو مُعَاوِيَةَ، حَدَّثَنَا هِشَامُ بْنُ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، قَالَتْ جَاءَتْ فَاطِمَةُ ابْنَةُ أَبِي حُبَيْشٍ إِلَى النَّبِيِّ ﷺ فَقَالَتْ يَا رَسُولَ اللَّهِ إِنِّي امْرَأَةٌ أُسْتَحَاضُ فَلاَ أَطْهُرُ، أَفَأَدَعُ الصَّلاَةَ فَقَالَ رَسُولُ اللَّهِ ﷺ " لاَ، إِنَّمَا ذَلِكِ عِرْقٌ، وَلَيْسَ بِحَيْضٍ، فَإِذَا أَقْبَلَتْ حَيْضَتُكِ فَدَعِي الصَّلاَةَ، وَإِذَا أَدْبَرَتْ فَاغْسِلِي عَنْكِ الدَّمَ ثُمَّ صَلِّي ". قَالَ وَقَالَ أَبِي " ثُمَّ تَوَضَّئِي لِكُلِّ صَلاَةٍ، حَتَّى يَجِيءَ ذَلِكَ الْوَقْتُ ".