Jesus never said to "pray for the sick". Jesus said to heal the sick.
Matthew 10:8Living Bible (TLB)
8 Heal the sick, raise the dead, cure the lepers, and cast out demons. Give as freely as you have received!
John 14:12-14Living Bible (TLB)
12-13 “In solemn truth I tell you, anyone believing in me shall do(this could be a command?) the same miracles I have done, and even greater ones, because I am going to be with the Father.
Mark 16:17-18King James Version (KJV)
17 And these signs shall follow them that believe; In my name shall they cast out devils; they shall speak with new tongues;
18 They shall take up serpents; and if they drink any deadly thing, it shall not hurt them; they shall (this could be a command?) lay hands on the sick, and they shall recover.
Jesus told "believers" to "do" something about the sick and dieing. He told believers to heal the sick and raise the dead. Even if we do not see anything happen, Jesus told us to go lay hands on the sick.
Here is another scripture passage which could be taken as a command.
Mark 16:17King James Version (KJV)
17 And these signs shall follow them that believe; In my name shall they cast out devils; they shall speak with new tongues;
Here is a sample "prayer"
In the name of Jesus, I speak to the cancer in this body and command it to leave this body, now, and never return. In the name of Jesus, I declare and I decree this body shall now be free of all works of the devil. I bless this body with the life of God. Thank you Jesus.
Our job as believers is to lay hands on sick people and speak in Jesus name the same things Jesus did. It is the Holy Spirits job to take it from there. We do our part, the Holy Spirit does His part. We do not need to see things "happen" immediately, we just need to do our part.
In the name of Jesus, I bless you with the life of God.