Hiring/Renting: Responsibility of a Butcher for Rendering an Animal Unlawful

Practical Laws of Islam as per the teachings of Ayatullah Sistani

Ruling 2211

If a butcher slaughters an animal in a manner that renders it unlawful [to consume], he must pay its value to the owner, regardless of whether he has taken a fee for slaughtering it or did it free of charge.

-Ayatullah Sistani, Practical Laws of Islam, Hiring/Renting (Ijarah)