Titus 1:15

All things are pure to the pure; but to the defiled and unbelieving nothing is pure; but both their mind and their conscience are defiled.

Romans 14:20

For the sake of meat do not destroy the work of God. All things indeed are pure; but it is evil to that man who eats while stumbling in doing so.

Romans 14:23

But he that doubts, if he eat, is condemned; because it is not of faith; but whatever is not of faith is sin.

Romans 14:14

I know, and am persuaded in the Lord Jesus, that nothing is unclean of itself; except to him who reckons anything to be unclean, to that man it is unclean.

Matthew 15:18

but the things which go forth out of the mouth come out of the heart, and those defile man.

Acts 10:15

And there was a voice again the second time to him, What God has cleansed, do not thou make common.

Proverbs 21:4

Lofty eyes, and a proud heart, the lamp of the wicked, is sin.

Haggai 2:13

And Haggai said, If one that is unclean by a dead body touch any of these, is it become 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 those seventy years, did ye really fast unto me, even unto me?

Luke 11:39-41

But the Lord said to him, Now do ye Pharisees cleanse the outside of the cup and of the dish, but your inward parts are full of plunder and wickedness.

1 Corinthians 6:12-13

All things are lawful to me, but all things do not profit; all things are lawful to me, but I will not be brought under the power of any.

1 Corinthians 8:7

But knowledge is not in all: but some, with conscience of the idol, until now eat as of a thing sacrificed to idols; and their conscience, being weak, is defiled.

1 Corinthians 10:23

All things are lawful, but all are not profitable; all things are lawful, but all do not edify.

1 Corinthians 10:25

Everything sold in the shambles eat, making no inquiry for conscience sake.

1 Corinthians 10:31

Whether therefore ye eat, or drink, or whatever ye do, do all things to God's glory.

1 Corinthians 11:27-29

So that whosoever shall eat the bread, or drink the cup of the Lord, unworthily, shall be guilty in respect of the body and of the blood of the Lord.

1 Timothy 4:3-4

forbidding to marry, bidding to abstain from meats, which God has created for receiving with thanksgiving for them who are faithful and know the truth.

1 Timothy 6:5

constant quarrellings of men corrupted in mind and destitute of the truth, holding gain to be the end of piety.

Hebrews 9:14

how much rather shall the blood of the Christ, who by the eternal Spirit offered himself spotless to God, purify your conscience from dead works to worship the living God?

Hebrews 10:22

let us approach with a true heart, in full assurance of faith, sprinkled as to our hearts from a wicked conscience, and washed as to our body 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
But the Lord said to him, Now do ye Pharisees cleanse the outside of the cup and of the dish, but your inward parts are full of plunder and wickedness.
Acts 10:15
And there was a voice again the second time to him, What God has cleansed, do not thou make common.
Romans 14:14
I know, and am persuaded in the Lord Jesus, that nothing is unclean of itself; except to him who reckons anything to be unclean, to that man it is unclean.
1 Corinthians 6:12
All things are lawful to me, but all things do not profit; all things are lawful to me, but I will not be brought under the power of any.
1 Corinthians 10:23
All things are lawful, but all are not profitable; all things are lawful, but all do not edify.
1 Timothy 4:3
forbidding to marry, bidding to abstain from meats, which God has created for receiving with thanksgiving for them who are faithful and know the truth.

Their

1 Corinthians 8:7
But knowledge is not in all: but some, with conscience of the idol, until now eat as of a thing sacrificed to idols; and their conscience, being weak, is defiled.
Hebrews 9:14
how much rather shall the blood of the Christ, who by the eternal Spirit offered himself spotless to God, purify your conscience from dead works to worship the living God?
Hebrews 10:22
let us approach with a true heart, in full assurance of faith, sprinkled as to our hearts from a wicked conscience, and washed as to our body with pure water.

General references

Leviticus 7:19
And the flesh that toucheth anything unclean shall not be eaten; it shall be burned with fire. And as to the flesh, all that are clean may eat the flesh.
Leviticus 10:10
that ye may put difference between the holy and the unholy, and between unclean and clean,
Leviticus 11:34
All food that is eaten on which such water hath come shall be unclean; and all drink that is drunk shall be unclean, in every such vessel.
Deuteronomy 14:3
Thou shalt not eat any abominable thing.
Acts 24:16
For this cause I also exercise myself to have in everything a conscience without offence towards God and men.