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 (ranked by relevance)
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.
Acts 8:2
And devout men carried Stephen to his burial, and made great lamentation over him.