俱舍論疏 15.39

15.39

論「由彼至親至有損害心」，答也。由彼作害一切羊意樂故，至親作羊亦起害心，故普於彼得不律儀。

The treatise says: "Because toward even their closest kin... they have an intention to harm."
This is the answer. Because their motivation is to harm all sheep, even if their closest kin were to become a sheep they would still give rise to an intention to harm; therefore, they acquire non-restraint universally in relation to them.