Add an option -o StrictHostKeyChecking=no into a ssh command:
ssh -o StrictHostKeyChecking=no your_username@example.com
OR
export TARGET_HOST='example.com'
if [ -z `ssh-keygen -F ${TARGET_HOST}` ]; then
ssh-keyscan -H ${TARGET_HOST} >> ~/.ssh/known_hosts
fi
ssh-keygen -R ${TARGET_HOST}
ssh-keyscan -f ~/.ssh/known_hosts ${TARGET_HOST} >>~/.ssh/known_hosts 2>/dev/null