Whoever associates with bad people will see no good.

If an angel associates with a demon
He will learn from him fear, fraud and hypocrisy.
Of the wicked thou canst learn only wickedness.
A wolf will not take to sewing jackets.

Saadi Shirazi

http://www.poemhunter.com/poem/ch-08-on-rules-for-conduct-in-life-maxim-24/