David fought the enemies of the Lord and the king recovered land that the Lord had given to Israel. One of the enemies David subdued was Zobah, and from them,

David took from him one thousand chariots, seven hundred horsemen, and twenty thousand foot soldiers. Also David hamstrung all the chariot horses, except that he spared enough of them for one hundred chariots (2 Samuel 8.4). 

Again, I believe we have an incidental reference to the number 7.