SURAH AL-KAHF: 5

TAFSIR AL-TABARI ON SURAH AL-KAHF: 5

وقوله : ( مَا لَهُمْ بِهِ مِنْ عِلْمٍ ) يقول: ما لقائلي هذا القول، يعني قولهم (اتَّخَذَ اللَّهُ وَلَدًا)(بِهِ ) : يعني بالله من علم، والهاء في قوله (بِهِ) من ذكر الله, وإنما معنى الكلام: ما لهؤلاء القائلين هذا القول بالله إنه لا يجوز أن يكون له ولد من علم، فلجهلهم بالله وعظمته قالوا ذلك.

http://quran.ksu.edu.sa/tafseer/tabary/sura18-aya5.html

TAFSIR AL-BAIDHAWI

مَا لَهُمْ بِهِ مِنْ عِلْمٍ أَيْ بِالْوَلَدِ أَوْ بِاتِّخَاذِهِ أَوْ بِالْقَوْلِ ، وَالْمَعْنَى أَنَّهُمْ يَقُولُونَهُ عَنْ جَهْلٍ مُفْرِطٍ وَتَوَهُّمٍ كَاذِبٍ ، أَوْ تَقْلِيدٍ لِمَا سَمِعُوهُ مِنْ أَوَائِلِهِمْ مِنْ غَيْرِ عِلْمٍ بِالْمَعْنَى الَّذِي أَرَادُوا بِهِ ، فَإِنَّهُمْ كَانُوا يُطْلِقُونَ الْأَبَ وَالِابْنَ بِمَعْنَى الْمُؤَثِّرِ وَالْأَثَرِ . أَوْ بِاللَّهِ إِذْ لَوْ عَلِمُوهُ لَمَا جَوَّزُوا نِسْبَةَ الِاتِّخَاذِ إِلَيْهِ .

http://library.islamweb.net/newlibrary/display_book.php?idfrom=1500&idto=1500&bk_no=205&ID=1520

MUHAMMAD ASAD: No knowledge whatever have they of Him, 2  and neither had their forefathers: dreadful is this saying that comes out of their mouths, [and] nothing but falsehood do they utter!

Note - 2

Most of the classical commentators (and, as far as I am aware, all the earlier translators of the Qur'an) relate the pronoun in bihi to the assertion that "God has taken unto Himself a son", and hence take the phrase to mean, "They have no knowledge of it", i.e., no knowledge of such a happening. However, this interpretation is weak inasmuch as absence of knowledge does not necessarily imply an objective negation of the fact to which it relates. It is, therefore, obvious that bihi cannot signify "of it": it signifies "of Him", and relates to God. Hence, the phrase must be rendered as above - meaning that they who make such a preposterous claim have no real knowledge of Him, since they attribute to the Supreme Being something that is attributable only to created, imperfect beings. This interpretation is supported, in an unequivocal manner, by Tabari and, as an alternative, by Baydawi.