Yesterday (here) I noted that the earliest explict source of a Jew being named at a Brit Milah seems to be from the Christain Bible. I was thinking about it a bit more, and now I wonder whether there was an earlier source, or if perhaps this source snuck in to classic works. The Tzitz Eliezer (18:54)cites the Otzar Kol Minhagei Yeshurun, citing the Otzar HaShemot that the minhag to only name the child at the Brit existed on Bayit Sheni.
וכפי שראיתי בספר אוצר כל מנהגי ישורון סימן מ”א אות ז’ הוא כותב בשם אוצר השמות שנדע כי כבר בימי הבית השני נהגו כן. לקרוא בשם להבן הנולד בעת המילה.
He seems to be referncing the passage in the tenth volume of Otzar HaShemot of Avraham Chaim Rosenberg – here – who claims that this custom has been around since the fourth century before the common era. He cites no proof for this assertion. Does anyone know who he was and what his source could have been? Could it be related to the Christain Bible, or perhaps some other source that is even earlier?