Luke 9:49-50:

And John answered and 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.

See also:

Mark 9:38-39
Notes on Mark 9:38-39
YOU Can Do Miracles
The Power in the Name of Jesus
Your Authority over Sickness
Who Can Lay Hands on the Sick in Mark 16, Apostles or All Believers?
Objection: Christ’s Disciples Were Told to Heal EVERYONE.  No One Does This Today, So We Cannot Say We Have the Same Authority They Did
Condition: Demon Possession