成唯識論述記 4.134

4.134

述曰：若言大乘是迦葉等餘佛語，非釋迦語，則極成許大乘是佛說。今佛亦應說此大乘；佛智等故；如迦葉等佛。何故乃言大乘非佛說翻覆自違？彼文廣論問答。又縱汝許是佛所說，不是佛說，皆有過失。

The Commentary states: If one says that the Mahāyāna is the word of other Buddhas such as Kāśyapa, and not the word of Śākyamuni, then it is universally established and accepted that the Mahāyāna is the Buddha's speech. The present Buddha should also speak this Mahāyāna; because the Buddha's wisdom is equal; like the Buddhas such as Kāśyapa. Why then do you turn around and contradict yourself by saying that the Mahāyāna is not the Buddha's speech? That text discusses questions and answers at length. Furthermore, whether you grant that it was spoken by a Buddha or not spoken by a Buddha, both incur fallacies.