Titus 1:15

To the pure all things are pure: but to them that are defiled and unbelieving nothing is pure; but both their mind and their conscience are defiled.

Romans 14:20

Overthrow not for meat's sake the work of God. All things indeed are clean; howbeit it is evil for that man who eateth with offence.

Romans 14:23

But he that doubteth is condemned if he eat, because he eateth not of faith; and whatsoever is not of faith is sin.

Romans 14:14

I know, and am persuaded in the Lord Jesus, that nothing is unclean of itself: save that to him who accounteth anything to be unclean, to him it is unclean.

Matthew 15:18

But the things which proceed out of the mouth come forth out of the heart; and they defile the man.

Acts 10:15

And a voice came unto him again the second time, What God hath cleansed, make not thou common.

Proverbs 21:4

A high look, and a proud heart, Even the lamp of the wicked, is sin.

Haggai 2:13

Then said Haggai, If one that is unclean by reason of a dead body touch any of these, shall it be unclean? And the priests answered and said, It shall be unclean.

Zechariah 7:5-6

Speak unto all the people of the land, and to the priests, saying, When ye fasted and mourned in the fifth and in the seventh month , even these seventy years, did ye at all fast unto me, even to me?

Luke 11:39-41

And the Lord said unto him, Now ye the Pharisees cleanse the outside of the cup and of the platter; but your inward part is full of extortion and wickedness.

1 Corinthians 6:12-13

All things are lawful for me; but not all things are expedient. All things are lawful for me; but I will not be brought under the power of any.

1 Corinthians 8:7

Howbeit there is not in all men that knowledge: but some, being used until now to the idol, eat as of a thing sacrificed to an idol; and their conscience being weak is defiled.

1 Corinthians 10:23

All things are lawful; but not all things are expedient. All things are lawful; but not all things edify.

1 Corinthians 10:25

Whatsoever is sold in the shambles, eat, asking no question for conscience'sake,

1 Corinthians 10:31

Whether therefore ye eat, or drink, or whatsoever ye do, do all to the glory of God.

1 Corinthians 11:27-29

Wherefore whosoever shall eat the bread or drink the cup of the Lord in an unworthy manner, shall be guilty of the body and the blood of the Lord.

1 Timothy 4:3-4

forbidding to marry, and commanding to abstain from meats, which God created to be received with thanksgiving by them that believe and know the truth.

1 Timothy 6:5

wranglings of men corrupted in mind and bereft of the truth, supposing that godliness is a way of gain.

Hebrews 9:14

how much more shall the blood of Christ, who through the eternal Spirit offered himself without blemish unto God, cleanse your conscience from dead works to serve the living God?

Hebrews 10:22

let us draw near with a true heart in fulness of faith, having our hearts sprinkled from an evil conscience: and having our body washed with pure 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 unto him, Now ye the Pharisees cleanse the outside of the cup and of the platter; but your inward part is full of extortion and wickedness.
Acts 10:15
And a voice came unto him again the second time, What God hath cleansed, make not thou common.
Romans 14:14
I know, and am persuaded in the Lord Jesus, that nothing is unclean of itself: save that to him who accounteth anything to be unclean, to him it is unclean.
1 Corinthians 6:12
All things are lawful for me; but not all things are expedient. All things are lawful for me; but I will not be brought under the power of any.
1 Corinthians 10:23
All things are lawful; but not all things are expedient. All things are lawful; but not all things edify.
1 Timothy 4:3
forbidding to marry, and commanding to abstain from meats, which God created to be received with thanksgiving by them that believe and know the truth.

Their

1 Corinthians 8:7
Howbeit there is not in all men that knowledge: but some, being used until now to the idol, eat as of a thing sacrificed to an idol; and their conscience being weak is defiled.
Hebrews 9:14
how much more shall the blood of Christ, who through the eternal Spirit offered himself without blemish unto God, cleanse your conscience from dead works to serve the living God?
Hebrews 10:22
let us draw near with a true heart in fulness of faith, having our hearts sprinkled from an evil conscience: and having our body washed with pure water,

General references

Leviticus 7:19
And the flesh that toucheth any unclean thing shall not be eaten; it shall be burnt with fire. And as for the flesh, every one that is clean shall eat thereof:
Leviticus 10:10
and that ye may make a distinction between the holy and the common, and between the unclean and the clean;
Leviticus 11:34
All food therein which may be eaten, that on which water cometh, shall be unclean; and all drink that may be drunk in every'such vessel shall be unclean.
Deuteronomy 14:3
Thou shalt not eat any abominable thing.
Acts 24:16
Herein I also exercise myself to have a conscience void of offence toward God and men always.

American Standard Version Public Domain