According to our traditions Abraham was loyal to all the commandments and also to all Rabbinic decrees see. So, when he served his visitors with dairy and meat foods [Genesis 18] Rashi explains this to mean that he served them dairy whilst the meat was being prepared. He certainly did not serve meat and dairy combined which is prohibited by Torah Law.

 

The Pesikta however proposes that he did combine and cook meat and milk which the Meshech Chochmah explains was not a breach of Biblical or Rabbinic law since it was BP meat which may be cooked with dairy. See also

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The enigmatic Pesikta depicts that the angels' protests, objecting to Gd presenting the Torah to His People, were quashed by reminding them that they ate the meat and dairy meal when visiting Avraham.

 

The Meshech Chochmah explains this - 

  *  Avraham will not cook an ordinary meat and dairy combination

  *  even if cooked in error he will not eat it nor serve it to guests

  *  he had a Ben PeKuAh animal that may be cooked with dairy

 

Now the angels were surprised by the menu as they too do not eat meat and dairy combinations and agreed to partake only because they were assured by Avraham that it was the meat of a Ben PeKuAh.

 

However, in order to produce a Ben PeKuAh, the first BP must be found in a Kosher slaughtered animal and Kosher slaughter can only be performed by one who is Jewish. Thus, the angels in accepting Abraham's invitation to eat, were conceding that he is Jewish and obviously has full rights to the Torah. In that case Abraham's children also have full rights to the Torah.

 

BTW the reference is to the meat of the BP and not its milk - which some argue is identical to the milk found in the udders of a Shechted cow which is not Halachically dairy. However, Rabbinic decree bans cooking meat in such milk and so Avraham Avinu who followed all Torah laws including Rabbinic decrees, would not have cooked meat in BP milk.  

See also R M Sterbuch here who quite clearly identifies that the Meshech Chochma is referring to teh meat of BP not its milk.

 

 

ויקח חמאה וחלב ובן הבקר אשר עשה

"'איתא בפסיקתא רבתי "משה חזור להם תשובה כו

"'הלא אכלתן בשר בחלב אצל אברהם אבינו כו"

והענין דאברהם קיים כל התורה כולה

וכפי הנראה דהבן הבקר היה בן פקועה ושחיטה התירתו

ואין בה משום בב"ח

דחלב שחוטה מותר

ועיין שעה"מ

ולכך ע"כ דיצא מכלל בני נח

דאי לאו הכי אסור עדיין משום בשר בחלב

ועוד דאין שחיטה מתירתו והוה אבר מן החי

וכיון דכבר נתקדש בקדושת התורה

מדוע תצעקו מה לילוד אשה בינינו

הלא שלו הוא נוטל

original    ועוד יש להאריך עפ"י דברי הט"ז