Matthew 10:15
Verily I say unto you, It shall be more tolerable for the land of Sodom and Gomorrha in the day of judgment, than for that city.
Cross-reference
In Matthew 11:22-24, Jesus repeats the same 'more bearable for Sodom' comparison, applying it to Chorazin and Bethsaida.
Matthew 11:24 repeats the same saying about Sodom on judgment day, applied to Chorazin and Bethsaida. Direct parallel.
Ezekiel 16:48-56 compares Jerusalem to Sodom, explaining Sodom's sins — providing OT background for why Sodom is the benchmark of judgment.
Mark 6:11 contains the parallel account of the sending, with the identical warning about Sodom on judgment day.
Luke 10:12 directly echoes the warning: 'it will be more bearable for Sodom than for that town.'
2 Peter 2:9 refers to God's judgment on the unrighteous, using Sodom as an example — reinforcing the certainty of judgment for rejecters.
Luke 9:5 is the parallel account of the same instruction: shaking off dust as testimony against rejecting towns. Synoptic parallel.
John 15:22-24 explains that greater revelation brings greater guilt — a parallel principle to why rejecting disciples brings severe judgment.