Galatians 1:9

What I have just said I repeat--if any one is preaching to you a Good News other than that which you originally received, let him be accursed.

Romans 16:17

But I beseech you, brethren, to keep a watch on those who are causing the divisions among you, and are leading others into sin, in defiance of the instruction which you have received; and habitually to shun them.

2 Corinthians 1:17

Did I display any vacillation or caprice in this? Or the purposes which I form--do I form them on worldly principles, now crying "Yes, yes," and now "No, no"?

2 Corinthians 13:1-2

This intended visit of mine is my third visit to you. "On the evidence of two or three witnesses every charge shall be sustained."

Philippians 3:1

In conclusion, my brethren, be joyful in the Lord. For me to give you the same warnings as before is not irksome to me, while so far as you are concerned it is a safe precaution.

Philippians 4:4

Always be glad in the Lord: I will repeat it, be glad.

Revelation 22:18-19

"I solemnly declare to every one who hears the words of the prophecy contained in this book, that if any one adds to those words, God will add to him the plagues spoken of in this book;

Treasury of Scripture Knowledge

Summary

As we said before, so say I now again, If any man preach any other gospel unto you than that ye have received, let him be accursed.

General references

Bible References

So

2 Corinthians 1:17
Did I display any vacillation or caprice in this? Or the purposes which I form--do I form them on worldly principles, now crying "Yes, yes," and now "No, no"?
2 Corinthians 13:1
This intended visit of mine is my third visit to you. "On the evidence of two or three witnesses every charge shall be sustained."
Philippians 3:1
In conclusion, my brethren, be joyful in the Lord. For me to give you the same warnings as before is not irksome to me, while so far as you are concerned it is a safe precaution.
Philippians 4:4
Always be glad in the Lord: I will repeat it, be glad.

Than

Revelation 22:18
"I solemnly declare to every one who hears the words of the prophecy contained in this book, that if any one adds to those words, God will add to him the plagues spoken of in this book;

General references

1 Corinthians 3:11
For no one can lay any other foundation in addition to that which is already laid, namely Jesus Christ.