Response A is closer to correct. The expression (or a close variant) is attested in Ben Jonson’s 1616 play The Devil Is an Ass; authoritative reference works (for example the Oxford English Dictionary and phrase-history sources) cite that play as the earliest printed instance.
Explanation
- Many modern dictionaries and phrase histories list Ben Jonson’s 1616 play as the earliest printed occurrence of the idiom in English (usually in an archaic spelling/wording). That is why you’ll often see the claim that the phrase dates to 1616.
- Important nuance: older printed texts often use slightly different wording or spelling, so some citations refer to a “variant” rather than the exact modern wording “when pigs fly.” In other words, Jonson’s play is cited for the same idea expressed with phrasing close to the contemporary idiom, rather than necessarily the verbatim modern phrase in exactly that orthography.
- Response B is incorrect to say there is “no evidence” — there is documentary evidence cited by lexicographers linking the idea/phrase to Jonson’s 1616 play.
If you want to check for yourself
- Look up the entry for “when pigs fly” (or for citations under the headword pig) in the Oxford English Dictionary — it lists early examples and their full citations.
- Consult a reliable edition or digital facsimile of Ben Jonson’s The Devil Is an Ass (1616) or Early English Books Online to see the original context and wording.