Since I had time now, I looked it up. It is on page 301 or pdf page 317 of the English translation of Maariful Quran (the pdf pages are not the same as the pages listed within the text). Directly quoting from Maariful: "The commentator al-Baydawi has remarked that, Allah being the First Cause of the things, the earlier Shari'ahs had allowed the use of the title "Father" for Him, but that the ignorant misunderstood and distorted the sense of "Fatherhood" so badly that to entertain such a belief or to apply this title to Allah has now been declared to be an act of infidelity (Kufr). As this practice can lead to all kinds of doctrinal disorders, it is no longer permissible to employ this particular word or a similar expression with reference to Allah."
Thank you for the reference. @ those with knowledge: just to clarify - does this refer to the shariah of previous prophets?