In the Shulchan Aruch Yoreh Deah 89, the rule is brought that after eating meat one may not eat cheese for 6 hours (other opinions are cited too, about how long to wait).
As far as I am aware, the practice is that this applies to drinking milk too.
What is the source for this? Perhaps the Halacha is a restriction on eating only, which involves chewing, but drinking is permitted?
The Rambam מאכלות אסורות in 9:28 mentions milk in place of cheese;
מִי שֶׁאָכַל בָּשָׂר בַּתְּחִלָּה בֵּין בְּשַׂר בְּהֵמָה בֵּין בְּשַׂר עוֹף לֹא יֹאכַל אַחֲרָיו חָלָב עַד שֶׁיִּהְיֶה בֵּינֵיהֶן כְּדֵי שִׁעוּר סְעֻדָּה אַחֶרֶת וְהוּא כְּמוֹ שֵׁשׁ שָׁעוֹת מִפְּנֵי הַבָּשָׂר שֶׁל בֵּין הַשִּׁנַּיִם שֶׁאֵינוֹ סָר בְּקִנּוּחַ:
Although he doesn’t use the word the “drink” he does change from the word cheese that the Gemara uses, to milk.
Rambam perek 4 shvuot halacha 3:
מִי שֶׁנִּשְׁבַּע שֶׁלֹּא יֹאכַל הַיּוֹם וְשָׁתָה חַיָּב שֶׁהַשְּׁתִיָּה בִּכְלַל אֲכִילָה. לְפִיכָךְ אִם אָכַל וְשָׁתָה אֵינוֹ חַיָּב אֶלָּא מַלְקוֹת אַחַת אִם הָיָה מֵזִיד אוֹ חַטָּאת אַחַת אִם הָיָה שׁוֹגֵג: When a person takes an oath that he will not eat on a specific day and drinks, he is liable, because [a prohibition against] eating includes drinking. Therefore, if he both ate and drank, he is liable only for one set of lashes if he acted willfully or one sin offering if he transgressed inadvertently.
Drinking is the same as eating.
