What is the ruling on the supplication (du'a) saying: "Ayat al-Kursi protects you," and is this considered shirk (polytheism), and is its speaker excused for his ignorance?

A Muslim's supplication for his brother to be protected by Ayat al-Kursi is permissible and not considered shirk (polytheism), because Ayat al-Kursi is from the words of Allah Almighty, and the words of Allah protect His servant. This is supported by the hadith: "Whoever stops at a place and then says: 'I seek refuge in the perfect words of Allah from the evil of what He has created,' nothing will harm him." And the perfect words of Allah are the Qur'an. Sheikh Ibn Uthaymeen clarified that the divinely prescribed words offer protection from all evil. Furthermore, it is mentioned in the virtue of Ayat al-Kursi that it protects its reciter from Satan until morning.