Sayyidah Khawlah bint Hakim (may Allah be pleased with her) said: I said: O Messenger of Allah, I menstruate and I have only one garment. He (peace and blessings be upon him) said: "Wash it and pray in it." I said: O Messenger of Allah, a trace of the blood remains in it. He (peace and blessings be upon him) said: "It does not harm you."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20985