Mahāyāna Mahāsaṃnipāta Kṣitigarbha Daśacakra Sūtra, Volume 6: Āśraya-parivarta

O virtuous man, therefore, if one wishes to seek liberation from birth and death within the Three Vehicles, delighting in peace and happiness while detesting danger and suffering, one should deeply believe in and revere the true Dharma spoken by the Tathagata—whether it is the true Dharma expounded according to the Sravakayana, or the true Dharma expounded according to the Pratyekabuddhayana, or the true Dharma expounded according to the Mahayana. Do not slander, obstruct, or conceal it, down to a single verse. Constantly be respectful, recite, and listen to it. One should arouse a firm and steadfast right vow seeking realization.

One should not dwell together with those who slander any one of the Dharmas of the Three Vehicles, even for a single night, nor should one associate with them to inquire, receive instructions, or listen to the Dharma. If any sentient beings, regarding the Three Vehicles, slander any one Vehicle, or further associate with those who slander the Three Vehicles to inquire, receive instructions, or listen to the Dharma, due to this cause, they shall certainly fall into the Avici hell, experiencing great suffering, with little hope of escape.

Why is this? O virtuous man, in the past when I cultivated the Bodhisattva conduct, diligently seeking to realize the supreme wisdom, whether it was for the sake of requesting even a single verse of the true Dharma expounded according to the Sravakayana, I would even abandon my own body, hands, feet, flesh, blood, skin, bones, head, eyes, marrow, and brain; or for the sake of requesting even a single verse of the true Dharma expounded according to the Pratyekabuddhayana, I would even abandon my own body, hands, feet, flesh, blood, skin, bones, head, eyes, marrow, and brain; or for the sake of requesting even a single verse of the true Dharma expounded according to the Mahayana, I would even abandon my own body, hands, feet, flesh, blood, skin, bones, head, eyes, marrow, and brain. Undergoing such hardship and toil, upon obtaining even a single verse of the Dharma within the Three Vehicles, I deeply rejoiced, respectfully received and upheld it, practiced according to the teachings without even momentary neglect. Through countless eons practicing all arduous and austere practices, I then realized the ultimate supreme fruit of wisdom. Furthermore, for the benefit and happiness of sentient beings, I proclaimed and expounded the true Dharma of the Three Vehicles. For this reason, one should not slander, obstruct, or conceal it, down to a single verse. Constantly be respectful, recite, and listen to it. One should arouse a firm and steadfast right vow seeking realization.

O virtuous man, this true Dharma, the essential path out [of suffering] of the Three Vehicles, has been jointly spoken by all the Buddhas of the past, future, and present, numerous as the sands of the Ganges. It is collectively protected by great majestic spiritual power, for the purpose of rescuing all sentient beings from the great suffering of birth and death, and for the purpose of perpetuating and glorifying the lineage of the Three Jewels so that it does not cease. Therefore, towards this true Dharma of the Three Vehicles, one should universally believe in and revere it. Do not slander, obstruct, or conceal it. If anyone slanders, obstructs, or conceals the true Dharma of the Three Vehicles, down to a single verse, they shall certainly fall into the Avici hell.

Explanation: The Buddhist sutra states that those who dwell together with someone who slanders even one of the Three Vehicles of the Buddha Dharma will also fall into the Avici hell. How much more so for those who spread slanderous statements against the Mahayana Dharma, propagate Theravada Buddhism, or propagate the Dharma teachings of Theravada masters—this is equivalent to destroying the Buddha's teachings, plunging sentient beings into the ocean of suffering, causing them to sink for endless kalpas. Therefore, the karmic obstruction is extremely profound, and liberation is difficult to attain.