Where is the Six True Words of Buddhism from

From The Buddha Speaks of the Mahayana Majestic Treasure King Sutra, Volume IV.

The Buddha Speaks of the Mahayana Majestic Treasure King Sutra, belongs to the classics of the Founder's Department. It is contained in the sixteenth volume of the Taisho Collection. It is a four-volume work translated by Tianshiqi in the Song Dynasty. It is a classic that mainly preaches the mantra of Guanyin Bodhisattva and the merits of Guanyin Bodhisattva. Among them, the Six Character Mantra is from the fourth volume.

The Six Character Daming Mantra, also known as Six Character Daming Dharani, Six Character Mantra, Six Character Truth, and Mani Mantra, is a mantra of the mind of Guanshiyin Bodhisattva, which originates from the Sanskrit language. This mantra contains the endless blessings and compassion of the Buddhas, and is the sound manifestation of the compassion and wisdom of the Buddhas. The Six Character Mantra is an expansion of the three characters "Buzzing and Humming", which is exceptionally rich in connotation and infinite in wonder, and contains the great power, wisdom, and compassion of the universe. This mantra is the subtle original mind of Guanyin Bodhisattva.