This is a short miracle tale from the 觀世音菩薩感應事跡實錄- A true record of A True Record of Guanyin's Response and Effect .https://book.bfnn.org/books/0530.htm
In brief, a man's daughter-in-law falls sick with tonsillitis. A monk teaches him a short prayer to guanyin. She recovers almost immediately. The interesting thing is that the prayer in the sutra is extremely popular in Japan, where it is known as the "Ten-Line Kannon Sutra" https://www.sotozen.com/eng/library/glossary/individual.html?key=ten_line_kannon_sutra
◎清朝有位鄧承沼，廣東省廣州市人，早年即受三皈五戒，康熙戊申年五月，他的大媳婦黃氏，喉嚨忽然生了雙鵝，約有十幾天吞嚥困難且痛苦，
During the Qing, there lived a certain Deng Chenzhao, a man from Guangzhou, Guangdong. He had in his youth taken refuge in the Triple Gem and took the Five Precepts. In the 5th month of the Wushen Year of Kangxi (1668), his daughter-in-law, maiden name Huang, had a pair of geese spring up in her throat (i.e. developed tonsilitis). For over ten days, swallowing anything brought her extreme pain.
有一天弘贊和尚還山，乘船經過他的家門，承沼遇見了，就把兒媳的病情告訴他，並請教他如何醫治，和尚答覆他說：「觀音大士的威嚴神靈，是不可思議的，且能夠以大無畏的精神，施救眾生。」乃立即授以觀音救生經十句：
One Day, the old monk Hongzan was returning to his monastery. He happened to pass by their house. When Chenzhao saw him, he told the monk of his daughter-in-law’s illness, and requested the monk to teach him how to cure the illness. The monk said “The power of Guanyin Mahasattva is indescribable. Through her power of bestowing fearlessness, she saves the massed beings” He then taught him the ten-sentences of the Guanyin Scripture to Save Life
「觀世音，南無佛，
與佛有因，與佛有緣.
佛法僧緣，常樂我淨.
朝念觀世音，暮念觀世音，
念念從心起，念念不離心。 」.
Guanshiyin! Namo Buddha!
With the buddha, a cause!
With the buddha, a connection!
Connections with the Buddha, Dharma and Sangha!
Ever delight in my purity!
Morning, think of Guanyin!
Evening, think of Guanyin!
Every thought comes from the mind!
Every thought does not depart from the mind!
承沼回家後即教導兒媳誦念，並叫她把經抄本放置床前，且臨睡前再誦一次。第二天兒媳醒來身體爽快，精神也安定多了。如此持誦到第二天夜半，她病瘡內的膿血潰爛且均流出，她欣喜的叫喚說：我的病痊癒了。於是趕緊將口漱淨，向大士像前虔誠叩頭禮拜。病情恢復之快速，更是舉家歡慶。一時遠近大廣為流佈：「大士慈悲力量，靈感報應特別神速。」（觀音慈林集）. Chengzhao then taught his daughter-in-law this scripture, and also asked her to make a copy of the scripture to place before the bed, and recite it once before sleeping. On the second day, his daughter-in-law began to feel better, and her mind at ease. Chanting like this until midnight of the second day, the thick blood and pus began in her swellings began to all flowed out. She shouted in delight “My illness is completely cured!” She quickly rinsed her mouth, and kowtowed to Guanyin in veneration. Her swift recovery caused her family even more joy. Far and wide, they proclaimed “Swift indeed is the Mahasattva’s compassionate strength, her numinous powers and spiritual response” (From Guanyin’s forest of compassion)