The Sūtra of the Great Vow of Kṣitigarbha Bodhisattva (Kṣitigarbha Sūtra) is a story about the Buddha teaching to his mother in the Palace of Trāyastriṃśa Heaven about the merits of Kṣitigarbha. It was translated into Chinese, assumedly from Sanskrit, by the monk Śiksānanda from Khotan circa 700....
At that time, from an unimaginable, indescribable, uncountable, unutterable, unlimted, asaṃkhyeya number of worlds and all the hells, the Kṣitigarbha division bodies assembled at the Palace of the Trāyastriṃśa Heaven. Through the Tathāgata's divine powers, each one of the division bodies, and all those that had obtained liberation from the path of karma and also each of the ten billion nayutas, all holding incense and flowers, came to make offerings to the Buddha. Because they had been taught and transformed by Kṣitigarbha Bodhisattva those that all came together would never regress from anuttara-samyak-sambodhi. They had acheived many levels, after long kalpas wandering through Saṃsāra through the Six Realms suffering hardships without even a temporary rest. Through Kṣitigarbha Bodhisattva's great compassion and strong unyielding will each one has realized their attainment. Since reaching Trāyastriṃśa Heaven, they were so overjoyed in admiration for the Tathāgata that and looked at him unblinkingly.
At that time, the World Honored One stretched out his golden arms and rubbed the heads of the division bodies from the unimaginable, indescribable, uncountable, indescribable, unlimited asaṃkhyeya number of worlds and said, “In the Sahā World I educate and transform stubborn sentient beings such as this, to lead their minds to overcome evil, give up evil ways and return to upright actions. Now, out of every ten only one or two still have some vices. For these I also divide into innumerable division bodies and use many various skillful means. Those with good roots listen and immediately believe and accept. Those with positive karmic results from good actions can be convinced to succeed through hard work. Those that are ignorant can only be converted after a long time. Those that have karma from serious wrongdoing will not show any respect. Thus for each of the beings of different levels and different ages, each with their own characteristics, I divide my body to save them. This I appear in the form of a male, a female, a deva, a dragon, a spirit, a ghost, a mountain, a forest, a stream, a river, a pool, a sprint, or a well for their benefit and so that each and every one can be saved. I may appear in the form of Sakra, Brahma, a wheel turning king, a lay Buddhist, a king, a minister, an official, a monk, a nun, an upasaka, an upasika, a Śrāvaka, an Arhat, a Pratyekabuddha, or a bodhisattva in order to convert and save them. I do not only appear in the form of a Buddha before people.
“Reflect that I have worked tirelessly and diligently suffering over many kaplas in order to save these sentient beings who are difficult to convert and bitterly suffer for their wrongdoing. They have not yet overcome their evil habits will receive karmic retribution [karmaphala]. If they degenerate into an evil destiny and are subject to great suffering, remember that her, at the Palace of Trāyastriṃśa Heaven, I have, with confidence, handed over their care to you until Maitreya is born in the Sahā World and comes to liberate all sentient beings and end all suffering, meeting with the Buddha as predicted.”
Then the division bodies of Kṣitigarbha Bodhisattva from all the worlds came together into one form. He wept with great distress and addressed the Buddha saying, “Since kalpas in the ancient past I have been guided and protected by the Buddha, who gave me inconceivable divine powers, and great wisdom. My division bodies extended to hundreds of billions of worlds, as many as grains of sand in the Ganges. In each of those worlds I transform into billions of bodies. Each body saves trillions of people, leading them to take refuge in and esteem the Triple Gem, leaving Saṃsāra for ever to the joy of Nirvāṇa. Even if there good deeds towards the Dhárma are very little, perhaps just one hair, one drop, one grain of sand, or one speck of dust, I will use that to save them and to obtain great benefit. I only wish that the World Honored One will not worry about the sentient beings in later lifetimes with evil karma.”
Thus he said to the Buddha three times, “I only wish that the World Honored One will not worry about the sentient beings in later lifetimes with evil karma.”
Then the Buddha praised Kṣitigarbha Bodhisattva saying, “Excellent! Excellent! I will help you in this, which you do so joyfully. Your achievements since ancient kalpas, since making the great vow, saving great numbers will soon be complete and you will attain enlightenment.”