Natyashastra
कार्यहास्यं तु विज्ञेयमसंबद्धप्रभाषणात् । अनर्थकैर्विकारैश्च तथा चाश्लीलभाषितैः ॥ १४१॥
Laughter caused by speech (vākya-hāsya) is to be understood as arising from incoherent talking, meaningless distortions, and the use of obscene language.
english translation
kAryahAsyaM tu vijJeyamasaMbaddhaprabhASaNAt । anarthakairvikAraizca tathA cAzlIlabhASitaiH ॥ 141॥
hk transliteration by Sanscript