Poeticus
| abhyAvartin |
I am sure you can find it from the Maha Upanishad yourself.
And, I'm sure you'd be intellectually honest to admit the fact that the context of the verse in the MU differs from its colloquial usage in modern-day, Hindu-unversalistic notions.
Either way, the context of its usage in the MU is no longer mainstream - its derivation is only superficial and used for referencing. Rather, ironically, the context of its application from the Hitopadesha is the one that is currently extant.
For further reading regarding the irony of its current usage, click here.
And, coincidently, I believe the "mighty Wiki" elaborates my points a little further in laymen terms:
In the Mahopanishad - 6.72 the verses are used to describe as one of the attributes of an individual who has attained the highest level of spiritual progress, and one who is capable of performing his wordly duties without attachment to material possessions.
In the Panchatantra - 5.3.37, which is a collection of animal fables,the verse is uttered from the mouth of a declared fool who is killed by his naivety, suggesting it as a symbol of impracticality.
The Hitopadesha - 1.3.71 goes a step further, and not once but twice demonstrates its usage by sub-versionists, as well as tendency of the gullible to fall for it.