Sayyidah Mu'adhah (may Allah be pleased with her) said that a woman asked Sayyidah Aishah (may Allah be pleased with her): Menstrual blood gets on the clothes, and even washing does not remove the traces? Sayyidah Aishah (may Allah be pleased with her) said: There is no harm.
It has also been narrated from the Prophet (peace and blessings be upon him) through two weak chains.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4115