All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
The jurists stated that cleaning oneself after defecation or urination does not have to be done immediately, rather, when there is a need for it, like when wanting to perform the prayer, and they said: “The obligation of cleansing after defecation or urination is only for the validity of the prayer.” They also said: “It is not an obligation to cleanse oneself immediately after defecation or urine; rather, it is permissible to delay it until one wants to perform ritual purity (ablution or Ghusl) or wants to perform the prayer.” They further said: “Cleansing oneself after defecation or urination does not have to be done immediately; rather, when one wants to perform the prayer or fears that the impurity will spread (outside its usual place).”
This implies that a woman in menses is not obligated to cleanse herself after defecting or urinating because she does not perform the prayer unless the discharge of the impurity leads to its spreading (outside its usual place) and her being stained by it.
Allaah Knows best.