大毘盧遮那成佛經疏 2.83

2.83

第五十四「云何鹽心？謂所思念彼復增加思念」者，如鹽性鹹，凡有所入處皆增鹽味。此人心亦如是，於所思事復加思念，如憶想欲色之時適生此意，還復自推求：是心由誰而生？作何相貌？觀此心未決，復念此推求之慮有何因緣？如是則無窮盡也。既覺知已，當一向安心諦理，務使穿徹。又心性離念，非憶度能知，不於分別之上更增心數也。

As for the fifty-fourth, “What is the salt-like mind? It refers to further adding thoughts to what has been thought”: Just as the nature of salt is salty, and wherever it enters it adds the flavor of salt, this person's mind is also like this: regarding an object that has been thought of, they further add thoughts. For example, when recollecting desire and form, as soon as this thought arises, they again investigate themselves: “By whom was this mind produced? What marks does it make?” While observing this mind without resolution, they further think: “What causes and conditions are there for this investigating thought?” In this way it is limitless. Having recognized it, one should exclusively set one's mind on the genuine truth, making it penetrate completely. Furthermore, the nature of mind is free from thought and cannot be known by conceptual speculation; one should not add further mental factors upon conceptual discrimination.