Surah 18. Al-Kahf, Ayah 5

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.

The attribution of a son "begotten" to Allah has no basis in fact or in reason. It is only a "word" or "saying" that issues out of their mouths. It is not even a dogma that is reasoned out or can be explained in any way that is consistent with the sublime attributes of Allah.