Contradiction with Exodus 23:1
Jeremiah 41:7 involves deception and a massacre, whereas Exodus 23:1 advises against spreading false reports or joining with the wicked.
Exodus 23:1: Thou shalt not raise a false report: put not thine hand with the wicked to be an unrighteous witness. [raise: or, receive]
Contradiction with Matthew 5:44
Jesus teaches to love your enemies and pray for those who persecute you, which contrasts with the act of murder in Jeremiah 41:7.
Matthew 5:44: But I say unto you, Love your enemies, bless them that curse you, do good to them that hate you, and pray for them which despitefully use you, and persecute you;
Contradiction with Romans 12:17
Encourages not repaying evil for evil, opposing the violent betrayal seen in Jeremiah 41:7.
Romans 12:17: Recompense to no man evil for evil. Provide things honest in the sight of all men.
Contradiction with 1 Peter 3:9
Instructs to not return evil for evil or insult for insult, conflicting with the actions of Ismael in Jeremiah 41:7.
1 Peter 3:9: Not rendering evil for evil, or railing for railing: but contrariwise blessing; knowing that ye are thereunto called, that ye should inherit a blessing.
Contradiction with Proverbs 3:29
Advises against plotting harm against a neighbor, directly opposed to the deceit and killing in Jeremiah 41:7.
Proverbs 3:29: Devise not evil against thy neighbour, seeing he dwelleth securely by thee. [Devise...: or, Practise no evil]