When working an ingot on an anvil, it doesn't matter what item you are holding in your main/offhand, it will count as hammer, even if there is no hammer inside the anvil.

https://github.com/TerraFirmaCraft/TerraFirmaCraft/blob/1.18.x/src/main/java/net/dries007/tfc/common/blockentities/AnvilBlockEntity.java#L202