وقال محمد لا يجوز إلا أن يكون اللحم الذي في الحيوان أقل مما هو المعقود عليه
Translation: Muhammad does not allow it unless the meat within the animal is less than the separated meat being exchanged.
Muhammad ibn al-Hasan permits the same-type meat-for-animal transaction only when the separated meat exceeds the meat within the animal. Under this analysis, an equal portion is matched with the animal's meat and the excess corresponds to other valuable components.
One must not confuse the live animal’s total weight with its meat yield. Bone, hide and other components mean these are not identical quantities. The commentary explains Muhammad’s condition as an attempt to avoid a forbidden surplus in the meat-for-meat component.