Date: 15 Tamuz 5591
From: Rabbi Moshe Sofer
To: Rabbi Yosef Ohel
The responsum addresses the halachic question of whether one who forgot to count Sefirat HaOmer at night and counted during the day can continue counting with a blessing, considering the differing opinions on whether Sefirat HaOmer nowadays is a biblical or rabbinic obligation.
Source: Shu"t Chasam Sofer Collected §19