Has the Sharia forbidden pouring hot water into the toilet for fear of harming the jinn? If this is not mentioned, then how do many scholars corroborate this view?

It is authentically reported in the Hadith that the Prophet, peace and blessings be upon him, said: "Indeed, these privies (places of excretion) are frequented (by jinn/devils). So when one of you enters, let him say: 'In the name of Allah.'" The meaning of "محتضرة" (muḥtaḍara) is that devils are present there because it is a place of impurity, uncovering of one's nakedness, and lack of remembrance of Allah. One should avoid anything that harms jinn and devils in these places, and seek protection from them through remembrances (adhkar) and by saying "Bismillah."