To cite brms in publications use:

  Paul-Christian Bürkner (2017). brms: An R Package for Bayesian
  Multilevel Models Using Stan. Journal of Statistical Software, 80(1),
  1-28. doi:10.18637/jss.v080.i01

A BibTeX entry for LaTeX users is

  @Article{,
    title = {{brms}: An {R} Package for {Bayesian} Multilevel Models Using {Stan}},
    author = {Paul-Christian Bürkner},
    journal = {Journal of Statistical Software},
    year = {2017},
    volume = {80},
    number = {1},
    pages = {1--28},
    doi = {10.18637/jss.v080.i01},
    encoding = {UTF-8},
  }

Paul-Christian Bürkner (2018). Advanced Bayesian Multilevel Modeling
with the R Package brms. The R Journal, 10(1), 395-411.
doi:10.32614/RJ-2018-017

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Advanced {Bayesian} Multilevel Modeling with the {R} Package {brms}},
    author = {Paul-Christian Bürkner},
    journal = {The R Journal},
    year = {2018},
    volume = {10},
    number = {1},
    pages = {395--411},
    doi = {10.32614/RJ-2018-017},
    encoding = {UTF-8},
  }

Paul-Christian Bürkner (2021). Bayesian Item Response Modeling in R
with brms and Stan. Journal of Statistical Software, 100(5), 1-54.
doi:10.18637/jss.v100.i05

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Bayesian Item Response Modeling in {R} with {brms} and {Stan}},
    author = {Paul-Christian Bürkner},
    journal = {Journal of Statistical Software},
    year = {2021},
    volume = {100},
    number = {5},
    pages = {1--54},
    doi = {10.18637/jss.v100.i05},
    encoding = {UTF-8},
  }