Sutta question "well-trained mind"

[Nibbida]

I heard a talk by a teacher that quoted something from the Pali Canon, to the effect of:

"A person's worst enemy is an untrained mind.
A person's greatest friend is a well-trained mind."

I can't find any sutta references. Can anybody think of any? Perhaps Dhammapada?

It sounds so familiar I feel like I'm missing something obvious.

Thanks,
Nibbida

[David N. Snyder]

It might be this one, verse 43 from Dhammapada:

43. "Neither mother, father, nor any other relative can do one greater good than one's own well-directed mind."

http://www.accesstoinsight.org/tipitaka ... .budd.html