There is no prescribed punishment for one who has intercourse with an animal.
حدثنا أحمد بن يونس أن شريكا وأبا الأحوص وأبا بكر بن عياش حدثوهم عن عاصم عن أبي رزين
ليس على الذي يأتي البهيمة حد
No references are available.
[Its chain is hasan] Tirmidhi narrated it, no. 1455, as a suspended narration (muallaq) from the hadith of Asim bin Bahdala with this wording, and Nasai criticized it in al-Kubra, no. 7341, with a criticism that does not undermine it. This report does not weaken the preceding hadith in its two wordings, nos. 4462 and 4464, because this report applies to one who has not been married (muhsan), while the hadith applies to one who has been married. And Allah knows best.