俱舍論疏 2.59

2.59

論「由五識身至名為無足」，第二正通難也。分別有三，五識唯一，故名無分別。如馬有四足，唯有一足亦名無足。

On the Śāstra's: "Because the five consciousness bodies... is called footless": this is the second part, directly resolving the difficulty. There are three conceptual discriminations, and the five consciousnesses possess only one; hence they are called "without conceptual discrimination." Just as a horse normally has four feet, but if it has only one foot it is also called "footless."