كتاب الحيض
3  
The Book of Menstruation
(13)
Chapter: It is recommended for the woman who is performing ghusl following menses to apply a piece of cloth scented with musk to the site of the bleeding
(13)
باب اسْتِحْبَابِ اسْتِعْمَالِ الْمُغْتَسِلَةِ مِنَ الْحَيْضِ فِرْصَةً مِنْ مِسْكٍ فِي مَوْضِعِ الدَّمِ ‏
Sahih Muslim 332 b

'A'isha reported:

A woman asked the Messenger of Allah (ﷺ) how he should wash herself after the menstrual period. He (the Holy Prophet) said: Take a cotton with musk and purity yourself, and the rest of the hadith was narrated like that of Sufyan.
وَحَدَّثَنِي أَحْمَدُ بْنُ سَعِيدٍ الدَّارِمِيُّ، حَدَّثَنَا حَبَّانُ، حَدَّثَنَا وُهَيْبٌ، حَدَّثَنَا مَنْصُورٌ، عَنْ أُمِّهِ، عَنْ عَائِشَةَ، أَنَّ امْرَأَةً، سَأَلَتِ النَّبِيَّ صلى الله عليه وسلم كَيْفَ أَغْتَسِلُ عِنْدَ الطُّهْرِ فَقَالَ ‏ "‏ خُذِي فِرْصَةً مُمَسَّكَةً فَتَوَضَّئِي بِهَا ‏"‏ ‏.‏ ثُمَّ ذَكَرَ نَحْوَ حَدِيثِ سُفْيَانَ ‏.‏
Reference : Sahih Muslim 332b
In-book reference : Book 3, Hadith 71
USC-MSA web (English) reference : Book 3, Hadith 648
  (deprecated numbering scheme)