I get that idea from Jesus in Matthew
Matthew 7:15-20 Beware of false prophets, who come to you in sheep’s clothing but inwardly are ravenous wolves. You will recognize them by their fruits. Are grapes gathered from thornbushes, or figs from thistles? So, every healthy tree bears good fruit, but the diseased tree bears bad fruit. A healthy tree cannot bear bad fruit, nor can a diseased tree bear good fruit. Every tree that does not bear good fruit is cut down and thrown into the fire. Thus, you will recognize them by their fruits.
I get the idea from Jesus in Luke
Luke 6:44 For every tree is known by his own fruit. For of thorns men do not gather figs, nor of a bramble bush gather they grapes.
I get the idea from Jesus in Mark
Mark 13:22 For false Christs and false prophets shall rise, and shall shew signs and wonders, to seduce, if it were possible, even the elect.
I get the idea from Jesus in John
John 3:21 But he that doeth truth cometh to the light, that his deeds may be made manifest, that they are wrought in God.
I get the idea from John
1John 4:1-3 Beloved, do not believe every spirit, but test the spirits to see whether they are from God, for many false prophets have gone out into the world. By this you will know the Spirit of God: every spirit that confesses that Jesus Christ has come in the flesh is from God, and every spirit that does not confess Jesus is not from God.
I get the idea from Paul
1Timothy 6:3-4 If anyone teaches a different doctrine and does not agree with the sound words of our Lord Jesus Christ and the teaching that accords with godliness, he is puffed up with conceit and understands nothing.
I get the idea from James
22 But be ye doers of the word, and not hearers only, deceiving your own selves.
23 For if any be a hearer of the word, and not a doer, he is like unto a man beholding his natural face in a glass:
24 For he beholdeth himself, and goeth his way, and straightway forgetteth what manner of man he was.
25 But whoso looketh into the perfect law of liberty, and continueth therein, he being not a forgetful hearer, but a doer of the work, this man shall be blessed in his deed.
26 If any man among you seem to be religious, and bridleth not his tongue, but deceiveth his own heart, this man's religion is vain.
27 Pure religion and undefiled before God and the Father is this, To visit the fatherless and widows in their affliction, and to keep himself unspotted from the world.
I get the idea from Peter
2 But there were false prophets also among the people, even as there shall be false teachers among you, who privily shall bring in damnable heresies, even denying the Lord that bought them, and bring upon themselves swift destruction.
2 And many shall follow their pernicious ways; by reason of whom the way of truth shall be evil spoken of.
3 And through covetousness shall they with feigned words make merchandise of you: whose judgment now of a long time lingereth not, and their damnation slumbereth not.
I get the idea from Jude
4 For there are certain men crept in unawares, who were before of old ordained to this condemnation, ungodly men, turning the grace of our God into lasciviousness, and denying the only Lord God, and our Lord Jesus Christ.