שולחן ערוך אורח חיים · סימן תקנ״ח

English

On Tisha Be-Av around afternoon time the sanctuary caught fire, and burned until the sun set on the tenth, [subsequently] for this reason the proper custom is not to eat meat, nor to drink wine on the night of the tenth or the day of the tenth. Rema Note: There are those who are strict until midday and no longer (Hagehot Maymoni). If Tisha be-Av fell on Shabbat and was pushed off until the first day [of the week], it is permitted to eat meat and drink wine on the second day [of the week], but the night is forbidden because of the mourning of the preceding day (Maharil).