Is it true that performing ghusl (ritual bathing) for janabah (major ritual impurity) with water only, then pouring this water over the body after bathing with water and soap, is an established practice of the Prophet, peace and blessings be upon him, for undoing magic and the evil eye?

Washing with water from ghusl al-janabah (ritual bath after sexual impurity) is not a means of healing from magic. This has not been mentioned in the Qur’an, nor in the Sunnah, nor in any narration from the righteous predecessors. Rather, healing from magic is sought through dhikr (remembrance of Allah), ruqyah (incantations), and authentic incantations found in the Qur’an and Sunnah.