Biblical Referenes for Mourning Customs

There are several references throughout the Bible to periods of mourning lasting for specified periods of time:

Genesis 50:7-10

⁷ So Joseph went up to bury his father. With him went up all the servants of Pharaoh, the elders of his household, and all the elders of the land of Egypt, ⁸ as well as all the household of Joseph, his brothers, and his father's household. Only their children, their flocks, and their herds were left in the land of Goshen. ⁹ And there went up with him both chariots and horsemen. It was a very great company. ¹⁰ When they came to the threshing floor of Atad, which is beyond the Jordan, they lamented there with a very great and grievous lamentation, and he made a mourning for his father seven days.

Numbers 20:29

²⁹ And when all the congregation saw that Aaron had perished, all the house of Israel wept for Aaron thirty days.

Deuteronomy 34:7-8

⁷ Moses was 120 years old when he died. His eye was undimmed, and his vigor unabated. ⁸ And the people of Israel wept for Moses in the plains of Moab thirty days. Then the days of weeping and mourning for Moses were ended.

1 Samuel 31:13

¹³ And they took their bones and buried them under the tamarisk tree in Jabesh and fasted seven days.

There are also many, many references to the tearing of clothes, wearing sackcloth, going barefoot, and covering the head. These are too numerous to quote here. See this website: 100 Bible Verses About Mourning.