Does the persistence of traces of stool after using water to cleanse oneself (istijmar) affect the validity of ghusl from janabah (major ritual impurity), and is ghusl considered invalid in this case?

Obsessive whispering (waswas) is one of the most severe afflictions that can strike a Muslim in their religion. The best cure for it is to completely disregard it and to refrain from returning to matters of worship about which one has doubted, especially when the whispering intensifies. As for ghusl al-janabah (ritual bath after sexual impurity), it has no relation to istijmar (cleaning with stones/tissue). If you perform a correct ghusl, and then impurity exits after the ghusl, or you felt its presence before the ghusl, then the ghusl al-janabah is valid. However, you should perform wudu (ablution) after cleaning yourself from the impurity. It has been reported from Al-Zuhri regarding such a case: "They should wash their private parts and perform wudu."