Hebrews 9:7

But into the second, the high priest alone went, once during the year, not without blood, which he offered for himself, and for the errors of the people:

Hebrews 9:25

Nor has he entered, that he should offer himself often, as the high priest enters the holy places every year with the blood of another:

Hebrews 10:3

There is, however, in these sacrifices, a remembrance of sins every year.

Hebrews 10:14

For by one offering, he has made a perfect and perpetual expiation for the sanctified.

Treasury of Scripture Knowledge

Summary

And this shall be an everlasting statute unto you, to make an atonement for the children of Israel for all their sins once a year. And he did as the LORD commanded Moses.

Bible References

Once a year

Hebrews 9:7
But into the second, the high priest alone went, once during the year, not without blood, which he offered for himself, and for the errors of the people:
Hebrews 10:3
There is, however, in these sacrifices, a remembrance of sins every year.