וַיִּקַּ֨ח חֶמְאָ֜ה וְחָלָ֗ב וּבֶן־הַבָּקָר֙ אֲשֶׁ֣ר עָשָׂ֔ה וַיִּתֵּ֖ן לִפְנֵיהֶ֑ם וְהֽוּא־עֹמֵ֧ד עֲלֵיהֶ֛ם תַּ֥חַת הָעֵ֖ץ וַיֹּאכֵֽלוּ׃
Dann nahm er dicke Milch und süße Milch und das junge Rind, das er hatte zubereiten lassen, und setzte es ihnen vor; er aber stand bei ihnen unter dem Baum, während sie aßen.
Rashi on Genesis
ויקח חמאה וגו AND HE TOOK חמאה, ETC. — but he did not bring bread, on account of Sarah becoming mentstruant; as the 'way of women' returned to her that day, and the dough became impure (Bava Metzia 87a).
Rashbam on Genesis
ויקח חמאה וחלב, according to the plain meaning of the text there was no need to report that Avraham supplied the bread which he had volunteered to serve these men. It was only necessary to list the additional items he served, seeing no mention had been made of them thus far.