'Forty Years' in the Bible

Ishbosheth Saul's son was forty years old when he began to reign over Israel, and reigned two years. But the house of Judah followed David.

David was thirty years old when he began to reign, and he reigned forty years.

And it came to pass after forty years, that Absalom said unto the king, I pray thee, let me go and pay my vow, which I have vowed unto the LORD, in Hebron.