Is lying about God by prohibiting what is lawful, mistakenly quoting Ibn al-Qayyim, and describing God’s Kursi (Chair/Footstool) in an unfitting manner considered disbelief? And how can one remember what is read in order to teach others, and get rid of such actions?

What was said is not a lie about Allah, but rather a lie and fabrication about Ibn al-Qayyim. Lying about people is not disbelief unless the one who says it considers it permissible. The prohibition against imagining the details and specific form of the Chair (Kursi) is correct, based on the words of Allah the Almighty: "And do not pursue that of which you have no knowledge." However, there is no harm in generally imagining its greatness, as the Prophet, peace and blessings be upon him, said: "The seven heavens compared to the Kursi are nothing but like a ring thrown in an empty desert, and the superiority of the 'Arsh (Throne) over the Kursi is like the superiority of that desert over the ring." This encourages reflection on the greatness of Allah's creations. The prohibition should be against imagining the Kursi as earthly chairs, not against imagining its greatness altogether.

To strengthen memory, one should review the fatwas related to this matter. It is advisable to strive for mastery of religious knowledge, memorize texts and speech, and be deliberate in speech and actions. One should not utter or act except after verification, and if a statement is attributed to someone one is unsure about, it should be followed by "or something close to that." When making a mistake, one should promptly correct it, repent, and seek forgiveness.