Mark 10:8

And they twain shall be one flesh: so then they are no more twain, but one flesh.

Cross-references

1 Corinthians 6:16 also quotes 'the two shall become one flesh' from Genesis, applying it to sexual union.

Ephesians 5:31 cites the full Genesis quote including 'the two will become one flesh', exactly as Jesus says here.

Ephesians 5:28 develops the one flesh concept: loving one's wife as one's own body flows from being united as one flesh.