It is narrated from Hazrat Aisha (may Allah be pleased with her) that the Prophet (peace and blessings be upon him) said regarding the woman "who, after attaining purity from her menstrual period, sees something that puts her in doubt" that this is blood from a vein.
Hadith Referenceمسند احمد / مسند النساء / 24428
Hadith Gradingحکم دارالسلام:إسناده ضعيف لجهالة أم أبى بكر