Titus 1:15

Unto the pure, are all things pure: but unto them that are defiled, and unbelieving, is nothing pure: but even the very minds and consciences of them are defiled.

Romans 14:20

Destroy not the work of God for a little meat's sake. All things are pure: but it is evil for that man, which eateth with hurt of his conscience.

Romans 14:23

For he that maketh conscience, is damned if he eat: Because he doth it not of faith. For whatsoever is not of faith, that same is sin.

Romans 14:14

For I know, and am full certified in the Lord Jesus, that there is nothing common of itself: but unto him that judgeth it to be common, to him it is common.

Matthew 15:18

But those things which proceed out of the mouth come from the heart, and they defile the man.

Acts 10:15

And the voice spake unto him again the second time, "What God hath cleansed that make thou not common."

Proverbs 21:4

A presumptuous look, a proud stomach, and the plowing of the ungodly is sin.

Haggai 2:13

Then said Haggai, "Now if one being defiled with a dead carcass, touch any of these: shall it also be unclean?"

Zechariah 7:5-6

"Speak unto all the people of the land, and to the priests, and say, 'When ye fasted and mourned in the fifth and seventh month, now this seventy years, did ye fast unto me?

Luke 11:39-41

And the Lord said to him, "Now do ye, O Pharisees, make clean the outside of the cup, and of the platter: but your inward parts are full of ravening and wickedness.

1 Corinthians 6:12-13

All things are lawful unto me: but all things are not profitable. I may do all things: but I will be brought under no man's power.

1 Corinthians 8:7

But every man hath not knowledge. For some suppose that there is an idol, until this hour, and eat as of a thing offered unto the idol, and so their consciences being yet weak are defiled.

1 Corinthians 10:23

All things are lawful unto me, but all things are not expedient. All things are lawful to me, but all things edify not.

1 Corinthians 10:25

Whatsoever is sold in the market, that eat, and ask no questions for conscience sake.

1 Corinthians 10:31

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

1 Corinthians 11:27-29

Wherefore whosoever shall eat of this bread, or drink of the cup unworthily, shall be guilty of the body and blood of the Lord.

1 Timothy 4:3-4

forbidding to marry, and commanding to abstain from meats, which God hath created to be received with giving thanks, of them which believe, and know the truth.

1 Timothy 6:5

and vain disputations of men with corrupt minds, and destitute of the truth, which think that lucre is godliness. From such, separate thyself.

Hebrews 9:14

How much more shall the blood of Christ - which through the eternal spirit, offered himself without spot to God - purge your consciences from dead works, for to serve the living God?

Hebrews 10:22

let us draw nigh with a true heart in a full faith sprinkled in our hearts, from an evil conscience, and washed in our bodies 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 to him, "Now do ye, O Pharisees, make clean the outside of the cup, and of the platter: but your inward parts are full of ravening and wickedness.
Acts 10:15
And the voice spake unto him again the second time, "What God hath cleansed that make thou not common."
Romans 14:14
For I know, and am full certified in the Lord Jesus, that there is nothing common of itself: but unto him that judgeth it to be common, to him it is common.
1 Corinthians 6:12
All things are lawful unto me: but all things are not profitable. I may do all things: but I will be brought under no man's power.
1 Corinthians 10:23
All things are lawful unto me, but all things are not expedient. All things are lawful to me, but all things edify not.
1 Timothy 4:3
forbidding to marry, and commanding to abstain from meats, which God hath created to be received with giving thanks, of them which believe, and know the truth.

Their

1 Corinthians 8:7
But every man hath not knowledge. For some suppose that there is an idol, until this hour, and eat as of a thing offered unto the idol, and so their consciences being yet weak are defiled.
Hebrews 9:14
How much more shall the blood of Christ - which through the eternal spirit, offered himself without spot to God - purge your consciences from dead works, for to serve the living God?
Hebrews 10:22
let us draw nigh with a true heart in a full faith sprinkled in our hearts, from an evil conscience, and washed in our bodies with pure water,

General references

Leviticus 7:19
The flesh that toucheth any unclean thing shall not be eaten, but burnt with fire: and all that be clean in their flesh, may eat flesh.
Leviticus 10:10
that ye may put difference between holy and unholy, and between unclean and clean,
Leviticus 11:34
All manner meat that is eaten, if any such water come upon it, it shall be unclean. And all manner drink that is drunk in all manner such vessels, shall be unclean.
Deuteronomy 14:3
Ye shall eat no manner of abomination.
Acts 24:16
And therefore study I to have a clear conscience toward God, and toward man also.