Harry Potter is told during his first year by Nearly Headless Nick that Slytherin House has won the House Cup for several years:
“Gryffindor have never gone so long without winning. Slytherin have got the cup six years in a row!” (PS7)
Later he thinks:
“If they won their next match, against Hufflepuff, they would overtake Slytherin in the House Championship for the first time in seven years. ” (PS13).