大乘起信論裂網疏 1.78

1.78

此更約能乘之人以顯所乘之法，故曰：言大乘者，文殊、普賢等一切大人之所乘也。夫一切眾生心，莫不具體相用三大，即此三大便名為乘。而九界眾生，不能盡此心大乘之用，枉作壞驢、羊、鹿、水牛諸乘。唯一切佛已乘此大乘到究竟地，一切菩薩皆乘此大乘乃入佛地，故必約眾生心以顯大乘義也。二立義分竟。

This further explains the dharma that is ridden in terms of the persons who are able to ride it; hence it is said: speaking of the 'Mahāyāna', it is that which is ridden by all great beings such as Mañjuśrī and Samantabhadra. The minds of all sentient beings without exception possess the three greatnesses of essence, attributes, and function; these three greatnesses are themselves named 'vehicle'. Yet sentient beings of the nine realms cannot exhaust this mind's function of the Mahāyāna, vainly making vehicles of broken donkeys, goats, deer, and water buffaloes. Only all Buddhas have already ridden this Mahāyāna to reach the ultimate stage, and all bodhisattvas ride this Mahāyāna to enter the Buddha stage; therefore, one must explain the meaning of the Mahāyāna in terms of the mind of sentient beings. The second section, setting forth the fundamental tenets, is finished.