Galatians 1:9

As we have said before, so I say again now, if any one is preaching to you a gospel contrary to what you received, let him be accursed!

Romans 16:17

I urge you, brethren, to take note of those who cause divisions and difficulties, contrary to the doctrine which you have learned; avoid them.

2 Corinthians 1:17

When I was planning this, did I do it lightly? Or do I make my plans in a fleshly manner so that in the same breath I say, "Yes, Yes" and "No, No"?

2 Corinthians 13:1-2

This is the third time I am coming to you. Every charge must be established by the evidence of two or three witnesses.

Philippians 3:1

Finally, my brethren, rejoice in the Lord. To write the same things to you again is no trouble to me, and it is a safeguard for you.

Philippians 4:4

Rejoice in the Lord always; again I will say, Rejoice!

Revelation 22:18-19

I warn everyone who hears the words of the prophecy of this book: if anyone adds to them, God will add to him the plagues described 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
When I was planning this, did I do it lightly? Or do I make my plans in a fleshly manner so that in the same breath I say, "Yes, Yes" and "No, No"?
2 Corinthians 13:1
This is the third time I am coming to you. Every charge must be established by the evidence of two or three witnesses.
Philippians 3:1
Finally, my brethren, rejoice in the Lord. To write the same things to you again is no trouble to me, and it is a safeguard for you.
Philippians 4:4
Rejoice in the Lord always; again I will say, Rejoice!

Than

Revelation 22:18
I warn everyone who hears the words of the prophecy of this book: if anyone adds to them, God will add to him the plagues described in this book,

General references

1 Corinthians 3:11
For no other foundation can any one lay than the one which is laid, which is Jesus Christ.