Hebrews 9:7

But [only] once a year the head priest goes alone into the inner room [i.e., Holy of Holies], and never without [animal] blood, which he offers [as a sacrifice] for himself and for the sins done in ignorance by the people.

Hebrews 9:25

Nor was it necessary for Him to offer Himself [to God] often, like the head priest does, who enters the Holy of Holies year after year with blood that belongs to others [i.e., the blood of animal sacrifices].

Hebrews 10:3

But those sacrifices were [only] a reminder of [the people's] sins year after year,

Hebrews 10:14

For by one offering [i.e., the sacrifice of Himself], Christ has made perfect forever those people who are being set apart for 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] once a year the head priest goes alone into the inner room [i.e., Holy of Holies], and never without [animal] blood, which he offers [as a sacrifice] for himself and for the sins done in ignorance by the people.
Hebrews 10:3
But those sacrifices were [only] a reminder of [the people's] sins year after year,