The Messenger of Allah ﷺ said regarding a woman who sees something troubling after purification, "It is merely a vein or some veins."Muhammad bin Yahya commented that "after purification" means after performing the ritual bath.
حدثنا محمد بن يحيى حدثنا عبيد الله بن موسى عن شيبان النحوي عن يحيى بن أبي كثير عن أبي سلمة عن أم بكر أنها أخبرت أن
قال رسول الله ﷺ في المرأة ترى ما يريبها بعد الطهر قال إنما هي عرق أو عروق قال محمد بن يحيى يريد بعد الطهر بعد الغسل
[Its chain is daif] Abu Dawud narrated it in the Book of Purification, in the chapter on what has been reported that the woman with prolonged bleeding should perform ghusl before every prayer, hadith no. 293, from the hadith of Yahya through this route, and Bayhaqi narrated it, 1/337, from the hadith of Shayban through this route. Umm Bakr is of unknown status, and the hadith has supporting narrations.