The longest mantra

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楞严咒叫佛顶光明，是佛的顶上化佛所说。所以是微妙不可思议的。每一句有每一句的用途，每一字有每一字的奥妙，都具足不可思议。「佛顶光明」就是表示咒的力量能破除一切黑暗，能成就一切功德

This is the longest mantra I have come across; To this day, monks and nuns in the Chinese Buddhist tradition, as well as many practitioners among the laity, recite the mantra every morning as an essential aspect of daily practice;