首楞嚴義疏注經 7.217

7.217

問：既是怨對，無感生義，何得用附而生，怨中有愛？答：託質須資愛想，殺害由乎先業。愛想無常，由業所起。始雖起愛，後變成憎，故遭其食。

Question: Since they are enemies and rivals, there is no principle of affectionate response to induce birth; how can they rely on adoption to be born, with love within enmity? Answer: Lodging in form requires the assistance of affectionate thought; slaughtering arises from previous karma. Affectionate thought is impermanent and arises from karma. Though love arises at first, it later turns to hatred, and therefore [the parents] are eaten by them.