Commentary for Taanit 52:2

בתשעה באב נגזר על אבותינו שלא יכנסו לארץ וחרב הבית בראשונה ובשניה ונלכדה ביתר ונחרשה העיר

WITH THE BEGINNING OF AB REJOICINGS ARE CURTAILED. DURING THE WEEK IN WHICH THE NINTH OF AB FALLS IT IS FORBIDDEN TO CUT THE HAIR AND TO WASH CLOTHES BUT ON THE THURSDAY IT IS PERMISSIBLE IN HONOUR OF THE SABBATH. ON THE EVE OF THE NINTH OF AB ONE MAY NOT PARTAKE OF A MEAL OF TWO COURSES NOR EAT MEAT NOR DRINK WINE.

Rashi on Taanit