Is cursing the mouthwash and sniffing—after forgetting them during ablution or ghusl—considered disbelief (kufr), and is it sufficient to utter the Two Testimonies on any occasion after the incident to return to Islam, or is the intention to enter Islam an essential condition?

Rinsing the mouth (Madmadah) and sniffing water into the nose (Istinshaq) during ablution (Wudu) and ritual bath (Ghusl) are recommended (Mustahabb) and not obligatory (Wajib). If a person repents for having sinned by neglecting them due to forgetfulness, then repentance erases the effect of the sin. The repentance of an apostate is by uttering the two testimonies of faith (Shahadatayn). If their apostasy was due to denying an obligatory act (fard), then their repentance, along with the Shahadatayn, must include affirming the denied obligatory act.