This verse, part of Surah Al-Kahf, critiques those who falsely claim Allah has a child. Its broader context relates to the Quraysh challenging the Prophet Muhammad (PBUH) with questions from Jewish rabbis, including about the People of the Cave, Dhul-Qarnayn, and the soul. The Surah itself begins by praising Allah for revealing the Qur'an as a straight guide, warning disbelievers, and giving good news to believers.

Specifically, verse 18:5 condemns the assertion of Allah having a son, a belief held by some pagan Arabs concerning angels or others. The phrase "مَا لَهُم بِهِۦ مِنْ عِلْمٍۢ وَلَا لِءَابَآئِهِمْ" (No knowledge have they of such a thing, nor had their fathers) emphasizes the utter lack of basis for this claim; it is not supported by revelation, reason, or tradition. Ibn Kathir highlights "كَبُرَتْ كَلِمَةًۭ تَخْرُجُ مِنْ أَفْوَٰهِهِمْ" (Mighty is the word that comes out of their mouths) to underscore the gravity and enormity of this blasphemous lie. The verse concludes, "إِن يَقُولُونَ إِلَّا كَذِبًۭا" (They utter nothing but a lie), affirming that such statements are pure fabrication.

Theological insight here establishes Allah's absolute transcendence (Tawhid) and refutes any association of partners or offspring with Him. It teaches that attributing human characteristics or familial relations to God is a grave falsehood, signifying a fundamental misunderstanding of divine nature and a profound intellectual dishonesty. This verse thus serves as a powerful condemnation of shirk (polytheism) and emphasizes the importance of truthfulness in matters of faith.

📚 Sources: Classical tafsir (multi-source)