Sunan Ibn Majah, Book 1, Hadith 689 (In-Book) ⓘ

It was narrated from Umm Bakr that: She was told that 'Aishah said: "The Messenger of Allah said concerning a woman who sees that which causes her doubt (i.e. some bleeding) after she becomes pure: 'That is a vein or veins.'" (Da'if)"What was meant by 'after becomes pure' is after having a bath (following the end of her period)."

حَدَّثَنَا مُحَمَّدُ بْنُ يَحْيَى، حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُوسَى، عَنْ شَيْبَانَ النَّحْوِيِّ، عَنْ يَحْيَى بْنِ أَبِي كَثِيرٍ، عَنْ أَبِي سَلَمَةَ، عَنْ أُمِّ بَكْرٍ، أَنَّهَا أَخْبَرَتْ أَنَّ عَائِشَةَ قَالَتْ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ فِي الْمَرْأَةِ تَرَى مَا يَرِيبُهَا بَعْدَ الطُّهْرِ قَالَ ‏ "‏ إِنَّمَا هِيَ عِرْقٌ أَوْ عُرُوقٌ ‏" ‏ ‏.‏ قَالَ مُحَمَّدُ بْنُ يَحْيَى يُرِيدُ بَعْدَ الطُّهْرِ بَعْدَ الْغُسْلِ ‏.‏