Hebrews 9:7

but only the high priest could enter the inner part, and he but once a year, and never without taking some victim's blood, to offer on his own behalf and for the sins committed through ignorance by the people.

Hebrews 9:25

Nor does he go in to offer himself over and over again, like the high priest who enters the sanctuary year after year, taking with him blood that is not his own,

Hebrews 10:3

They really only serve to remind the people annually of the sins they have committed,

Hebrews 10:14

For by that one sacrifice he has forever qualified those who are purified from sin to approach God.

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 only the high priest could enter the inner part, and he but once a year, and never without taking some victim's blood, to offer on his own behalf and for the sins committed through ignorance by the people.
Hebrews 10:3
They really only serve to remind the people annually of the sins they have committed,