Hebrews 9:7

but into the second or inner part nobody but the high priest may go, and he only once a year, and never without blood which he offers for himself and for the sins committed in ignorance by the people.

Hebrews 9:25

And He does not enter to offer Himself over and over again, as the high priest enters the sanctuary year after year with blood that is not his own;

Hebrews 10:3

On the other hand, through these sacrifices there is given a real reminder of their sins,

Hebrews 10:14

For by that one sacrifice He has made perfect for all time those who are consecrated to Him.

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 or inner part nobody but the high priest may go, and he only once a year, and never without blood which he offers for himself and for the sins committed in ignorance by the people.
Hebrews 10:3
On the other hand, through these sacrifices there is given a real reminder of their sins,