1 Kings 2:11

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

2 Samuel 5:4-5

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

1 Chronicles 29:26-27

Now David the son of Jesse reigned over all Israel.

Treasury of Scripture Knowledge

Summary

And the days that David reigned over Israel were forty years: seven years reigned he in Hebron, and thirty and three years reigned he in Jerusalem.

Bible References

Reigned over

2 Samuel 5:4
David was thirty years old when he became king, and he reigned forty years.
1 Chronicles 29:26
Now David the son of Jesse reigned over all Israel.