From the Bible:

Gospel of St. Luke, Chapter 9:

And John…said, Master, we saw one casting out devils in thy name; and we forbad him, because he followeth not with us.

And Jesus said unto him, Forbid him not: for he that is not against us is for us.

From the Bhagavad Gita, third Chapter:

Trying even unsuccessfully to fulfill one’s own spiritual duty (dharma) is better than pursuing successfully the duties of others. Better death itself in the pursuance of one’s own duties. The pursuance of another’s duties is fraught with (spiritual) danger.