Was it wrong to tell a friend the truth about the Ash'aris and the Maturidis, and is it permissible for him to continue studying under scholars from these sects whom they respect, knowing that they do not preach their false beliefs?

Ahl al-Sunnah show mercy to creation and know the truth. The Ash'aris and Maturidis are the closest factions of the theologians to the methodology of the Salaf. Despite their errors, many of them served knowledge, and we benefit from the useful knowledge they left behind. We hope for their forgiveness. The truth should be taught to people gently, and the error of the mistaken person should be clarified without belittling them. One should seek forgiveness for them and supplicate for their guidance. The العلامة Al-Shanqeeti advised forgiving the error of scholars who interpreted the attributes (of Allah) because they thought they were purifying Allah. The questioner should adhere to the creed of Ahl al-Sunnah wa al-Jama'ah, advise scholars who have erred with gentleness and politeness, benefit from them in the sciences they have mastered, and supplicate for their guidance.