俱舍論疏 28.39

28.39

論「此因不成許有色故」，大眾部、化地部等難也。汝以無色故總名無色。無色之因我宗不許，許有色故，是不成過。

The Śāstra says: "This reason is unproven, because [we] accept that there is material form." This is an objection by the Mahāsāṃghika, Mahīśāsaka, and others: You state that because they lack material form, they are generally named 'formless.' The reason of 'lacking material form' is not accepted by our school, because we accept that there is material form; thus it incurs the fault of being unproven (asiddha).