Dungeon ni Deai o Motomeru no wa Machigatte Iru Darou ka Gaiden - Sword Oratoria - Ch. 128 - Memoria Freese

[MangaDex]

 

[Alx-Jeager115]

I guess this is a part that the main novel doesn't tell you, that Bell participated in it, and it's only on Ais' side.