Abu Dawud
Purification (Kitab Al-Taharah)
Book Number: 001 / Hadith Number: 360
Narated By Asma, daughter of Abu Bakr : I heard a woman asking the Apostle of Allah (pbuh): What should any of us do with her clothe (in which she menstruated) when she becomes purified? Can she pray in that (clothe)? He said: She should see; if she finds blood in it, she should scratch it with some water and (in case of doubt) sprinkle upon it (some water) and pray so long as she does not find (any blood).