"The Chain of Aforgomon" is a short story by Clark Ashton Smith.
A narrator recollects about the occult writings of an acquaintance of his named John Milwarp and how they have all mysteriously vanished from the libraries following his death, as even his recollection of him has become obscure. In his will, John made the narrator his executor and how he wanted him to spread interest in publishing for his newest novel, which is his diary, which he kept a while before his demise, and to the narrator, might explain how it happened.
Milwarp had returned to his house in San Francisco after a long sojourn in Indo-China into places that are obscured by the Occidentals. We who knew him gathered that he had gone into places seldom visited by Occidentals. Around the time of his death, he finished a novel dealing with more romantic and mysterious aspects of Burma. On the morning of April 2nd, 1933, his housekeeper noticed a glare of brilliant light which issued from the half-open door of Milwarp's study, and when investigating, she saw Milwarp sitting in an armchair at the table wearing Chinese brocade robes as a dressing-gown. When she confronted him, he removed the robe to find his body made of pure white fire in the form of linked chains. Though it stopped, the housekeeper, despite being frightened, saw that he was dead and scorch marks resembling long unbroken spirals were around his arms and legs, like he was being wrapped with chains. People have been figuring out the cause of death, chemists trying through a drug that Milwarp had been addicted to with an alkaloid whose source and attributes were obscure to Western science. They eventually gave up and memory of him has been obscured. His diary manuscript was given to the narrator, and he has been trying to decipher it before the ink of the text dissipates.
The text seemed to have unintelligible lettering as eventually he found that it told of the drug, called souvara, which is believed to restore, even for the uninitiate, the memory of other lives, obtaining it from Buddhists and first took it on March 9th. His physical vision was extended into seeing through objects and in altered coloration and he soon saw the history of Earth rewind up into the beginning of the universe, arriving in a mysterious city called Kalood on Hestan, a planet with four suns, seeing jewel-colored insects, beautiful gardens, and he was in an astronomic-themed robe. He was at an altar with symbols of Aforgomon, the omnipotent time-god, whom he was serving as his priest, and having the name Calaspa. He believed this to be a previous life and that he blasphemed them for the death of his wife Belthoris, summoning the dark sage and sorcerer Atmox. But he refused to aid him and tried to talk him out of it with no avail. He opened a manuscript book and learned of an incantation of the chief cosmic power antagonistic to Aforgomon, Xexanoth. He defiled the altar and began the demonolatrous ritual. He asked for one last hour with Belthoris and spent the full hour with her swearing that nothing could tear them apart.
When the hour was up, he was back with Atmox, and the souvara wore off with Milwarp waking up a day later, showing sorrow for Calaspa. The next entry of his diary begins with a strange dating in English script: 'The second day of the moon Occalat, in the thousand-and-ninth year of the Red Eon.', repeated in the language of Hestan with a line of unknown ciphers set apart beneath, then suddenly resumed in English. Calaspa's spell had seemed to reverse time for a brief period. Atmox had called upon a malign spirit concerned for the future, as it claimed that a rift would open soon for this maligh spirit, with Atmox warning Calaspa of it.
On the fourth day of the moon Occalat, Calaspa was recovering from the blood loss from his ritual, and was told that Aforgomon was angry. But he was later informed that Atmox's had been killed by an unseen monster as his neophytes saw his torn-apart body. Calaspa believed it to be the demon he summoned. On the fifth day of the moon Occalat, the priests of the altar arrested Calaspa and, on the sixth day of the moon Occalat, he was put into an oubliette as the high-priest Helpenor called upon Aforgomon for judgment. Aforgomon claimed that his punishment would be through fiery chains even in future incarnations and that a rift would forbid him from ever seeing Belthoris again, killing him in every incarnation.
On March 29th, Milwarp kept himself from souvara for two days, fearing he would suffer Calaspa's fate, but he has still returned to the oubliette in Hestan twice, as he fears gravely for what will occur. On the eighteenth day of the moon Occalat, Helpenor and three other priests took Calaspa to the adytum of Aforgomon. He was escorted to a gulf to be executed for his crimes. The holy chains of Aforgomon had wrapped around him, burning his flesh, and pulled into the gulf. He has thus suffered this punishment for eternity by present day, resulting in the death of John Milwarp.