From: Rabbi Moshe Sofer
To: Unknown recipient
Two shochtim swore not to slaughter in each other's territory; one violated the oath. The Chasam Sofer rules the shechitah is valid, demonstrating that the 'la mahani' principle does not apply to invalidate shechitah performed in violation of a private oath, and limiting its scope to Torah prohibitions involving specific items where self-divestiture truly occurs. He also provides a practical solution whereby the offending shochet takes a new oath before annulment of the original, protecting his colleague's interests.
Source: Shu"t Chasam Sofer YD §6