To cite rstanarm in publications use:

Stan Development Team (2016). rstanarm: Bayesian applied regression modeling via Stan. R package version 2.13.1. http://mc-stan.org/.

Corresponding BibTeX entry:

  @Misc{,
    title = {rstanarm: {Bayesian} applied regression modeling via
      {Stan}.},
    author = {{Stan Development Team}},
    note = {R package version 2.13.1},
    year = {2016},
    url = {http://mc-stan.org/},
  }