Date: 13 Tishrei 5584
From: Rabbi Moshe Sofer
To: Rabbi Yisrael
The Chasam Sofer rules that a father who reinforced his appointment of a specific mohel with a tekias kaf may not retract it, as the local rabbi who released the commitment erred gravely. The tekias kaf cannot be dissolved because the father foresaw the competing chevras sandekaos from the outset, the commitment was made on another's reliance with tangible consideration, tekias kaf is more stringent than an ordinary oath, and the retraction caused the mohel concrete financial loss and public humiliation.
Source: Shu"t Chasam Sofer YD §246