1 Kings 2:11

and the days that David hath reigned over Israel are forty years, in Hebron he hath reigned seven years, and in Jerusalem he hath reigned thirty and three years.

2 Samuel 5:4-5

A son of thirty years is David in his being king; forty years he hath reigned;

1 Chronicles 29:26-27

And David son of Jesse hath 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
A son of thirty years is David in his being king; forty years he hath reigned;
1 Chronicles 29:26
And David son of Jesse hath reigned over all Israel,