Titus 1:15

To the clean in heart all things are clean: but to those who are unclean and without faith nothing is clean; they become unclean in mind and in thought.

Romans 14:20

Do not let the work of God come to nothing on account of food. All things are certainly clean; but it is evil for that man who by taking food makes it hard for another.

Romans 14:23

But he who is in doubt is judged if he takes food, because he does it not in faith; and whatever is not of faith is sin.

Romans 14:14

I am conscious of this, and am certain in the Lord Jesus, that nothing is unclean in itself; but for the man in whose opinion it is unclean, for him it is unclean.

Matthew 15:18

But the things which come out of the mouth come from the heart; and they make a man unclean.

Acts 10:15

And the voice came to him a second time, What God has made clean, do not you make common.

Proverbs 21:4

A high look and a heart of pride, *** of the evil-doer is sin.

Haggai 2:13

Then Haggai said, Will any of these be made unclean by the touch of one who is unclean through touching a dead body? And the priests answering said, It will be made unclean.

Zechariah 7:5-6

Say to all the people of the land and to the priests, When you went without food and gave yourselves to grief in the fifth and the seventh months for these seventy years, did you ever do it because of me?

Luke 11:39-41

And the Lord said to him, You Pharisees make the outside of the cup and the plate clean; but inside you are thieves and full of evil.

1 Corinthians 6:12-13

I am free to do all things; but not all things are wise. I am free to do all things; but I will not let myself come under the power of any.

1 Corinthians 8:7

Still, all men have not that knowledge: but some, being used till now to the image, are conscious that they are taking food which has been offered to the image; and because they are not strong in the faith, their minds are troubled.

1 Corinthians 10:23

We are free to do all things, but there are things which it is not wise to do. We are free to do all things, but not all things are for the common good.

1 Corinthians 10:25

Whatever meat may be had at the public market, take as food without question of right or wrong;

1 Corinthians 10:31

So then, if it is a question of food or drink, or any other thing, whatever you do, do all to the glory of God.

1 Corinthians 11:27-29

If, then, anyone takes the bread or the cup of the Lord in the wrong spirit, he will be responsible for the body and blood of the Lord.

1 Timothy 4:3-4

Who keep men from being married and from taking food which God made to be taken with praise by those who have faith and true knowledge.

1 Timothy 6:5

Bitter talk of men who, being evil in mind and dead to what is true, take the faith to be a way of making profit.

Hebrews 9:14

How much more will the blood of Christ, who, being without sin, made an offering of himself to God through the Holy Spirit, make your hearts clean from dead works to be servants of the living God?

Hebrews 10:22

Let us go in with true hearts, in certain faith, having our hearts made free from the sense of sin and our bodies washed with clean water:

Treasury of Scripture Knowledge

Summary

Unto the pure all things are pure: but unto them that are defiled and unbelieving is nothing pure; but even their mind and conscience is defiled.

Bible References

The pure

Luke 11:39
And the Lord said to him, You Pharisees make the outside of the cup and the plate clean; but inside you are thieves and full of evil.
Acts 10:15
And the voice came to him a second time, What God has made clean, do not you make common.
Romans 14:14
I am conscious of this, and am certain in the Lord Jesus, that nothing is unclean in itself; but for the man in whose opinion it is unclean, for him it is unclean.
1 Corinthians 6:12
I am free to do all things; but not all things are wise. I am free to do all things; but I will not let myself come under the power of any.
1 Corinthians 10:23
We are free to do all things, but there are things which it is not wise to do. We are free to do all things, but not all things are for the common good.
1 Timothy 4:3
Who keep men from being married and from taking food which God made to be taken with praise by those who have faith and true knowledge.

Their

1 Corinthians 8:7
Still, all men have not that knowledge: but some, being used till now to the image, are conscious that they are taking food which has been offered to the image; and because they are not strong in the faith, their minds are troubled.
Hebrews 9:14
How much more will the blood of Christ, who, being without sin, made an offering of himself to God through the Holy Spirit, make your hearts clean from dead works to be servants of the living God?
Hebrews 10:22
Let us go in with true hearts, in certain faith, having our hearts made free from the sense of sin and our bodies washed with clean water:

General references

Leviticus 7:19
And flesh touched by any unclean thing may not be taken for food: it is to be burned with fire; and as for the flesh of the peace-offerings, everyone who is clean may take it as food:
Leviticus 10:10
And make a division between the holy and the common, and between the unclean and the clean;
Leviticus 11:34
Any food in it, and anything on which water from it comes, will be unclean: any drink taken from such a vessel will be unclean.
Deuteronomy 14:3
No disgusting thing may be your food.
Acts 24:16
And in this, I do my best at all times to have no reason for shame before God or men.

Basic English, produced by Mr C. K. Ogden of the Orthological Institute - public domain