The passuk in Parshas Vayechi states upon the passing of Yaakov Avinu, “And he [Yosef] made for his father a state of mourning for seven days.”
The Pirkie D’Rebbi Eliezer says that this is the source of the practice of Shiva in which a family member of a deceased person mourns their passing.
Rabbi Aharon Dovid Singer
Rosh Kollel, NMB Kollel
305-972-6508