(133) باب الْمَرْأَةِ تَغْسِلُ ثَوْبَهَا الَّذِي تَلْبَسُهُ فِي حَيْضِهَا
'Aishah said:
Each of us (wives of the Prophet) had only one clothe in which she would menstruate. Whenever it was smeared with blood, she would moisten it with her saliva and scratch it with saliva.
Reference: Sunan Abi Dawud 358
In-book reference: Book 1, Hadith 358
English translation: Book 1, Hadith 358