1 Chronicles 29:27

The time that he reigned over Israel was forty years; he reigned seven years in Hebron and thirty-three years in Jerusalem.

2 Samuel 5:4-5

David was thirty years old when he became king, and he reigned forty years.

1 Kings 2:11

The time that David reigned over Israel was forty years: he reigned seven years in Hebron and thirty-three years in Jerusalem.

1 Chronicles 3:4

These six were born to David in Hebron; he reigned there seven years and six months, and in Jerusalem he reigned thirty-three years.

Treasury of Scripture Knowledge

Summary

And the time that he reigned over Israel was forty years; seven years reigned he in Hebron, and thirty and three years reigned he in Jerusalem.

Bible References

Forty years

1 Chronicles 3:4
These six were born to David in Hebron; he reigned there seven years and six months, and in Jerusalem he reigned thirty-three years.
2 Samuel 5:4
David was thirty years old when he became king, and he reigned forty years.
1 Kings 2:11
The time that David reigned over Israel was forty years: he reigned seven years in Hebron and thirty-three years in Jerusalem.