Luke 10:8-9:

And into whatever city ye enter, and they receive you, eat such things as are set before you:
And heal the sick that are therein, and say unto them, The kingdom of God is come nigh unto you.

Notes on Luke 10:8-9:

Some places receive you better than others.  Jesus urged His disciples to minister where they were received and to leave places where they were not received.  I believe that NOT staying where no one receives you is what Jesus meant when He said not to cast your pearls before swine.  (Matthew 7:6: “Give not that which is holy unto the dogs, neither cast ye your pearls before swine, lest they trample them under their feet, and turn again and rend you.”)  However, you don’t have to have a crowd following you right away.  Paul preached at Ephesus and started with about a dozen people (Acts 19:7 says, “And all the men were about twelve”).  The fact that his initial crowd was only a dozen didn’t stop him from staying there for months.  Ephesus became the site of unusual miracles as things progressed (Acts 19:11-12).

Jesus did not order His disciples to do any modern act of “praying for the sick;” He ordered them to HEAL the sick.  This proves that they had the authority to do so.  Whenever Jesus commissioned preachers, He told them to HEAL the sick, not PRAY FOR the sick.  That is still the pattern today now that we have His delegated authority – we are to HEAL the sick, not just PRAY FOR the sick.  Our prayers would be for the enlightenment of the sick people, not requests for God to heal them, as He has already made provision for that and He has authorized us to use the name of Jesus to distribute that provision.  Technically, you can HEAL the sick without any prayer whatsoever; you can simply take authority over the sickness and command it to leave in the name of Jesus.

See also:

YOU Can Do Miracles
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: Anything Else Not Listed Here