(24) بَابُ إِذَا حَاضَتْ فِي شَهْرٍ ثَلاَثَ حِيَضٍ وَمَا يُصَدَّقُ النِّسَاءُ فِي الْحَيْضِ وَالْحَمْلِ فِيمَا يُمْكِنُ مِنَ الْحَيْضِ
Narrated `Aisha:
Fatima bint Abi Hubaish asked the Prophet, "I got persistent bleeding (in between the periods) and do not become clean. Shall I give up prayers?" He replied, "No, this is from a blood vessel. Give up the prayers only for the days on which you usually get the menses and then take a bath and offer your prayers."
Reference: Sahih al-Bukhari 325
In-book reference: Book 6, Hadith 30
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 6, Hadith 322