1 Kings 2:11

And the days that David reigned over Israel [were] forty
years
So says Eupolemus ^F19, an Heathen writer, which are thus reckoned:

seven years reigned he in Hebron;
the six months over are omitted, ( 2 Samuel 5:5 ) ; this part of his reign was over Judah only:

and thirty three years reigned he in Jerusalem;
over the twelve tribes, in all forty, which round number is only given; though in fact he reigned six months more.