To cite brms in publications use:

Paul-Christian Bürkner (in press). brms: An R Package for Bayesian Multilevel Models using Stan. Journal of Statistical Software.

Corresponding BibTeX entry:

  @Article{,
    title = {{brms}: An {R} Package for Bayesian Multilevel Models
      using Stan},
    author = {Paul-Christian Bürkner},
    journal = {Journal of Statistical Software},
    year = {in press},
    encoding = {UTF-8},
  }