Surdas or Sur was a blind Hindu poet and mystic of the 16th century.  Very little is know of his life, and it is likely that much of the large volume of work attributed to him was written by later poets in his name.  Nevertheless, he was highly regarded and very influential, and was part of the Bhakti [devotion] movement that represented a spiritual awakening of the masses.  The verse given here was included in the Sikh scripture, the Guru Granth Sahib.  It advises the devotee to avoid companions who are not focused on God, but this can refer not only to those around us but also to our own thoughts and impulses.

Turn away, mind, from those who turn from Hari.*
What’s the good in giving cobras milk?**
Snakes never lose their venom.
Why waste camphor† feeding it to crows
or squander Ganges water washing dogs?
Why go plastering perfume on an ass
or covering a monkey with jewels?
Empty your quiver, but arrows cannot pierce
a stone that’s fallen to the ground.
Surdas says, once a blanket’s dyed black,
it never takes on a different hue.

*Literally ‘Remover of distress or pain’; a title of Vishnu, Krishna or Ram.
**Milk is offered to snakes to propitiate them in the Hindu festival of Nag Panchami.
†Camphor was traditionally inhaled by singers to improve the voice.

Tr. John Stratton Hawley