Musnad Ahmad 30:1646

Musa ibn Dawud al-Dabbi narrated to us, Ibn Lahi'ah narrated to us, from Ubayd Allah ibn Abi Ja'far, from Isa ibn Talhah, from Abu Hurairah, that Khawlah bint Yasar came to the Prophet, peace and blessings of Allah be upon him, and said: "O Messenger of Allah, I have only one garment, and I menstruate in it." He said: "When you become pure, wash the place of the blood, then pray in it." She said: "O Messenger of Allah, if its trace does not come out?" He said: "The water is sufficient for you, and its trace will not harm you."