Date: 27 Elul 5571
From: Rabbi Moshe Sofer
To: Rabbi Yisrael
The responsum addresses the case of a firstborn son whose 30th day falls on Sukkot, and since pidyon haben cannot be performed on Yom Tov, the question is whether it can be done on the eve of Yom Tov with a condition, or if it must be delayed until Chol HaMoed.
Source: Shu"t Chasam Sofer Collected §7