Mark 9:45

And if thy foot offend thee, cut it off: it is better for thee to enter halt into life, than having two feet to be cast into hell, into the fire that never shall be quenched:

Cross-reference

In Mark 9:43, the same warning applies to the hand — both verses teach cutting off the offending member to avoid hellfire.

Mark 9:44 depicts the unquenchable fire of hell — the very punishment that Mark 9:45 warns will result from sin.