Why on Shabbos do most people daven (pray) later than usual? (I seek an halachic answer.)
The Ramah poskins based on a Mordecai in Shabbos in the name of Reb Hai Gaon on the posuk
וּבְיוֹם הַשַּׁבָּת שְׁנֵי כְבָשִׂים בְּנֵי שָׁנָה תְּמִימִם וּשְׁנֵי עֶשְׂרֹנִים סֹלֶת מִנְחָה בְּלוּלָה בַשֶּׁמֶן וְנִסְכּוֹ:
He says since during the weekday Korbon Tamid it says the word בבוקר and here it says וביום השבת it implies that on Shabbos we should daven later. The Mishnah Berurah argues and says Based on Rashi In Meggilah (Daf:Chuf Gimmel) that on Shabbos you should prefrably also Daven Vasikin and he ends off of course adding even according to the Ramah you would still have to make Zman Kriyas Shemah.