Hebrews 9:7

but into the second, the high priest alone, once a year, not without blood, which he offers for himself and for the ignorances of the people;

Hebrews 9:25

nor yet, that He should many times offer Himself, as the high priest enters into the Holies every year with blood not His own;

Hebrews 10:3

But in these sacrifices there is a remembrance of sins year by year;

Hebrews 10:14

For by one offering He hath perfected forever those who are being 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, once a year, not without blood, which he offers for himself and for the ignorances of the people;
Hebrews 10:3
But in these sacrifices there is a remembrance of sins year by year;