It is narrated from Sayyidah Aishah al-Siddiqah (may Allah be pleased with her): One of us women would have a long shirt in which she menstruated or became in a state of major impurity (janabah); then, if she saw a drop of blood on it, she would rub it off with her saliva.
(b) This is about a small amount of blood, which is excused; as for a large amount, it is authentically reported from her that she used to wash it. Its evidence will come in its proper place, if Allah wills.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 39