Numbers 20:29

And when all the congregation saw that Aaron was dead, they mourned for Aaron thirty days, even all the house of Israel.

Cross References

Deuteronomy 34:8 And the children of Israel wept for Moses in the plains of Moab thirty days: so the days of weeping and mourning for Moses were ended.
Genesis 1:10 And God called the dry land Earth; and the gathering together of the waters called he Seas: and God saw that it was good.
2 Chronicles 35:24-25 His servants therefore took him out of that chariot, and put him in the second chariot that he had; and they brought him to Jerusalem, and he died, and was buried in one of the sepulchres of his fathers. And all Judah and Jerusalem mourned for Josiah. And Jeremiah lamented for Josiah: and all the singing men and the singing women spake of Josiah in their lamentations to this day, and made them an ordinance in Israel: and, behold, they are written in the lamentations.
Acts 8:2 And devout men carried Stephen to his burial, and made great lamentation over him.