It is narrated from Talq bin Habib (may Allah have mercy on him) that a woman wrote to Sayyiduna Abdullah bin Abbas (may Allah be pleased with him) seeking a ruling about her bleeding, which had continued for two years, and she wrote earnestly adjuring him that if he had knowledge he should inform her of it. He said: "She should sit out the time of her menstruation, then take a ritual bath and pray." Two months had not passed over her before she became pure.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحيض / 1588