Sahih al-Bukhari 310
Sahih al-Bukhari · Book 6: Menstrual Periods · The I'tikaf of a woman who is bleeding in between her periods
Narrated `Aisha:
حَدَّثَنَا قُتَيْبَةُ ، قَالَ حَدَّثَنَا يَزِيدُ بْنُ زُرَيْعٍ ، عَنْ خَالِدٍ ، عَنْ عِكْرِمَةَ ، عَنْ عَائِشَةَ ، قَالَتِ اعْتَكَفَتْ مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم امْرَأَةٌ مِنْ أَزْوَاجِهِ، فَكَانَتْ تَرَى الدَّمَ وَالصُّفْرَةَ، وَالطَّسْتُ تَحْتَهَا وَهْىَ تُصَلِّي.
"One of the wives of Allah's Messenger (ﷺ) joined him in I`tikaf and she noticed blood and yellowish discharge (from her private parts) and put a dish under her when she prayed."