Psalm 12:2

They speak falsehood everyone with his neighbor. With flattering lip, and with a double heart, they speak.

Psalm 41:6

And if he comes to see [me], he speaks falsehood. His heart gathers iniquity to itself. When he goes abroad, he tells it.

Romans 16:18

For such kind serve not our Lord Jesus Christ, but their own belly. And by their smooth words and elegant speech they deceive the hearts of the naive.

Psalm 10:7

His mouth is full of cursing and deceit and oppression. Under his tongue is mischief and iniquity.

Jeremiah 9:8

Their tongue is a deadly arrow; it speaks deceit. He speaks peaceably to his neighbor with his mouth, but in his heart he lays wait for him.

1 Chronicles 12:33

Of Zebulun, such as were able to go out in the army, who could set the battle in array, with all manner of instruments of war, fifty thousand, and who could order [the battle array, and were] not of double heart.

Psalm 5:9

For there is no faithfulness in their mouth. Their inward part is very wickedness. Their throat is an open sepulcher. With their tongue they {deceive (LXX/NT)}.

Psalm 28:3

Draw me not away with the wicked, and with the workers of iniquity, who speak peace with their neighbors, but mischief is in their hearts.

Psalm 144:8

whose mouth speaks deceit, and whose right hand is a right hand of falsehood.

James 1:8

a double-minded man, unstable in all his ways.

Psalm 36:3-4

The words of his mouth are iniquity and deceit. He has ceased to be wise [and] to do good.

Psalm 38:12

Those also who seek after my life lay snares [for me]. And those who seek my hurt speak mischievous things, and meditate deceits all the day long.

Psalm 52:1-4

Why boast thou thyself in mischief, O mighty man? The loving kindness of God [is] continual.

Psalm 55:21

His mouth was smooth as butter, but his heart was war. His words were softer than oil, yet they were drawn swords.

Psalm 59:12

[for] the sin of their mouth, [and] the words of their lips. Let them even be taken in their pride, and for cursing and lying which they speak.

Psalm 62:4

They only consult to thrust him down from his dignity. They delight in lies. They bless with their mouth, but they curse inwardly. Selah.

Psalm 144:11

Rescue me, and deliver me out of the hand of aliens, whose mouth speaks deceit, and whose right hand is a right hand of falsehood.

Proverbs 20:19

He who goes about as a tale-bearer reveals secrets. Therefore do not associate with him who opens wide his lips.

Proverbs 29:5

A man who flatters his neighbor spreads a net for his steps.

Jeremiah 9:2-6

Oh that I had in the wilderness a lodging-place of wayfaring men, that I might leave my people, and go from them! For they are all adulterers, an assembly of treacherous men.

Ezekiel 12:24

For there shall no more be any FALSE vision nor flattering divination within the house of Israel.

1 Thessalonians 2:5

For we came neither in word of flattery (at any time as ye know) nor a pretense of greed (God is witness)

Treasury of Scripture Knowledge

Summary

They speak vanity every one with his neighbour: with flattering lips and with a double heart do they speak.

A double heart

Bible References

Flattering

Psalm 5:9
For there is no faithfulness in their mouth. Their inward part is very wickedness. Their throat is an open sepulcher. With their tongue they {deceive (LXX/NT)}.
Psalm 28:3
Draw me not away with the wicked, and with the workers of iniquity, who speak peace with their neighbors, but mischief is in their hearts.
Psalm 62:4
They only consult to thrust him down from his dignity. They delight in lies. They bless with their mouth, but they curse inwardly. Selah.
Proverbs 20:19
He who goes about as a tale-bearer reveals secrets. Therefore do not associate with him who opens wide his lips.
Proverbs 29:5
A man who flatters his neighbor spreads a net for his steps.
Ezekiel 12:24
For there shall no more be any FALSE vision nor flattering divination within the house of Israel.
Romans 16:18
For such kind serve not our Lord Jesus Christ, but their own belly. And by their smooth words and elegant speech they deceive the hearts of the naive.
1 Thessalonians 2:5
For we came neither in word of flattery (at any time as ye know) nor a pretense of greed (God is witness)

A double heart

1 Chronicles 12:33
Of Zebulun, such as were able to go out in the army, who could set the battle in array, with all manner of instruments of war, fifty thousand, and who could order [the battle array, and were] not of double heart.

General references

Genesis 29:19
And Laban said, It is better that I give her to thee, than that I should give her to another man. Abide with me.
Judges 16:6
And Delilah said to Samson, Tell me, I pray thee, in what thy great strength lays, and with what thou might be bound to afflict thee.
Habakkuk 1:3
Why do thou show me iniquity, and look upon perverseness? For destruction and violence are before me, and there is strife, and contention rises up.
Acts 12:22
And the populace shouted, The voice of a god, and not of a man.