1 Chronicles 29:27
And the days that he reigned over Israel [were] forty years. In Hebron he reigned seven years, and in Jerusalem he reigned thirty-three years.
2 Samuel 5:4-5
David [was] thirty years old when he began to reign; he reigned forty years.
1 Kings 2:11
The days that David reigned over Israel [were] forty years; he reigned seven years in Hebron and thirty-three years in Jerusalem.
1 Chronicles 3:4
Six were born to him in Hebron. And he reigned there seven years and six months. And he reigned thirty-three years in Jerusalem.
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.                        
                    Forty years
Bible References
Forty years
                                        1 Chronicles 3:4                                        
                                                                                                                                Six were born to him in Hebron. And he reigned there seven years and six months. And he reigned thirty-three years in Jerusalem.
                                    
                                        2 Samuel 5:4                                        
                                                                                                                                David [was] thirty years old when he began to reign; he reigned forty years.
                                    
                                        1 Kings 2:11                                        
                                                            
                        The days that David reigned over Israel [were] forty years; he reigned seven years in Hebron and thirty-three years in Jerusalem.