Hebrews 9:7

but the second tent is entered only once a year by the high priest alone ??and it must not be without blood, which he presents on behalf of himself and the errors of the People.

Hebrews 9:25

Nor was it to offer himself repeatedly, like the high priest entering the holy place every year with blood that was not his own: ??26 for in that case he would have had to suffer repeatedly, ever since the world was founded. Nay, once for all, at the end of the world, he has appeared with his self-sacrifice to abolish sin.

Hebrews 10:3

As it is, they are an annual reminder of sins

Hebrews 10:14

For by a single offering he has made the sanctified perfect for all time.

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 the second tent is entered only once a year by the high priest alone ??and it must not be without blood, which he presents on behalf of himself and the errors of the People.
Hebrews 10:3
As it is, they are an annual reminder of sins