Babylonian Talmud, Kiddushin 40a

R. Zadok was summoned by a certain matron [to have sex with her.] Said he to her, 'My heart is faint and I am unable; is there aught to eat?' She answered him, 'There is unclean food.' 'What am I to deduce from this?' She then fired the oven and was placing it [the forbidden meat] therein, when he ascended and sat in it. Said she to him, 'What is the meaning of this?' 'He who commits the one [sexual immorality] falls into the other [the fire - of Gehenna / hell]', was his reply. 'Had I know that it is so heinous,' said she, 'I would not have tormented you'. [Soncino translation]