Hebrews 9:7

but into the second only the high-priest went once a year; and that not without blood, which he offered for himself, and for the sins of the people committed through ignorance.

Hebrews 9:25

nor to offer Himself often, as the high-priest entereth into the holy of holies every year with the blood of others;

Hebrews 10:3

Whereas in these very sacrifices there is a recalling of sins to mind every year.

Hebrews 10:14

For by one offering He hath perfected for ever those that are 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 only the high-priest went once a year; and that not without blood, which he offered for himself, and for the sins of the people committed through ignorance.
Hebrews 10:3
Whereas in these very sacrifices there is a recalling of sins to mind every year.