Language:
كتاب الحيض
6  
Menstrual Periods
(10)
Chapter: The I'tikaf of a woman who is bleeding in between her periods
(10)
باب الاِعْتِكَافِ لِلْمُسْتَحَاضَةِ
Sahih al-Bukhari 310

Narrated `Aisha:

"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."

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.‏
Reference : Sahih al-Bukhari 310
In-book reference : Book 6, Hadith 15
USC-MSA web (English) reference : Vol. 1, Book 6, Hadith 307
  (deprecated numbering scheme)