Seven Days of Mourning

בראשית נ, י דַע ואֹּבָ

ירושלמי מסכת מועד קטן דף יג/ב פרק ג הלכה ה גמרא מנין לאבילות שבעה מן התורה, שנאמר ויעש לאביו אבל שבעת ימים

How could we learn a law from prior to the giving of Torah? Thus, the Talmud Bavli derives from another verse (Amos 8)הפכתי חגיכם לאבל , just like the standard holiday is a 7-day period, also mourning is a 7-day period. Perhaps, the difference between the two Talmuds would be reflected in regards to the status of מלאכה during Chol HaMoed, if compared to mourning or not.

According to the consensus, these cited verses are only a אסמכתא, and the 7-day mourning period is a rabbinical decree. According to the Torah the law of mourning applies only to the day of the burial.