Themison has no wife — and never missed her.
Fabullus, you ask why? He has a sister.

[Quare non habeat, Fabulle, quaeris
Uxorem Themison? Habet sororem.]

Martial (AD c.39-c.103) Spanish Roman poet, satirist, epigrammatist [Marcus Valerius Martialis]

Epigrams [Epigrammata], Book 12, epigram 20 (12.20) (AD 101) [tr. McLean (2014)]
    (Source)

"To Fabullus." Both Ker and Shackleton Bailey explicitly note that habet does, in fact, have a secondary meaning of "has sex with." (Source (Latin)). Alternate translations:

You lately were inquiring, why Silvester
Has not yet got a wife? -- He has a sister.
[tr. Hay (1755)]

Why Themison has not a wife, nor e'er missed her,
Fabullus, you ask? Honest Them has a sister.
[tr. Elphinston (1782)]

Do you ask, Fabullus, why Themison has not a wife? He has a sister.
[tr. Bohn's Classical (1859)]

Do you ask, Fabullus, why Themison has not got a wife? He has a sister.
[tr. Ker (1919)]

You wonder how he lives unmarried? Cease
To marvel, for his Reverence has a niece.
[tr. Pott & Wright (1921), "The Alternative"]

Do you ask, dear reader, why Themison
     Has no wife? Why, hell!
The reason's rather obvious:
     His sister does as well!
[tr. Marcellino (1968)]

Brother never
     had a wife
he had sister
     all his life.
[tr. Goertz (1971)]

Fabullus, you ask why Themison doesn't have a wife. He has a sister.
[tr. Shackleton Bailey (1993)]

Why no wife? He quickly concedes
His sister takes care of all his needs.
[tr. Ericsson (1995)]

Of course we know he'll never wed.
What? Put his sister out of bed?
[tr. Wills (2007)]

He doesn't need a wife
His sister is enough
[tr. Kennelly (2008), "Enough"]

You want to know, Fabullus, why Themison doesn’t have a wife. He has a sister.
[tr. @aleatorclassicus (2010)]

Fabullus, do you want to know why Mr.
Themison has no wife? He has a sister.
[tr. Powell]