Contradiction with Matthew 5:14-16
Jesus instructs believers to let their light shine before others, which contrasts with the instruction of secrecy in Mark 8:26.
Matthew 5:14-16: Ye are the light of the world. A city that is set on an hill cannot be hid.
Contradiction with Luke 8:39
After healing the demon-possessed man, Jesus tells him to return to his house and declare what God has done for him, which is the opposite of Jesus's instruction in Mark 8:26.
Luke 8:39: Return to thine own house, and shew how great things God hath done unto thee. And he went his way, and published throughout the whole city how great things Jesus had done unto him.
Contradiction with Mark 5:19
Jesus tells a man healed from demons to go home and tell his friends what the Lord has done, contradicting the command for silence in Mark 8:26.
Mark 5:19: Howbeit Jesus suffered him not, but saith unto him, Go home to thy friends, and tell them how great things the Lord hath done for thee, and hath had compassion on thee.