From: Rabbi Moshe Sofer
To: Rabbi Ephraim Zalman Margolios
Rabbi Ephraim Zalman Margalios sought to use the RABaN's ruling that left-foot chalitzah is valid b'dieved as a supporting factor to validate an actual case. The Chasam Sofer firmly rejects this, demonstrating that the RABaN stands alone against all other poskim, making him a yachid b'makom rabim, and that relying on a lone minority opinion against the majority is impermissible for a Torah-level prohibition even in cases of urgent need.
Source: Shu"t Chasam Sofer EH II §71