Martin Luther says that Christians are to:
“… grieve more over the sin of their offenders than over the loss or offense to themselves. And they do this that they may recall these offenders from their sin rather than avenge the wrongs they themselves have suffered. Therefore they put off the form of their own righteousness and put on the form of those others, praying for their persecutors, blessing those who curse, doing good to the evildoers, preparing to pay the penalty and make satisfaction for their very enemies that they may be saved. This is the gospel….” [italics added]
Luther doesn’t simply equate the “gospel” with justification by faith alone, but includes “praying,” “blessing,”and “doing good.” In this quote, Luther seems to be saying that one must not only affirm sola fide, one must also live it out in real life.