  We present a fully differential description of a decay of a scalar Higgs
boson into massive b-quarks valid at next-to-next-to-leading order (NNLO) in
perturbative quantum chromodynamics (QCD). We work within the nested
soft-collinear subtraction scheme extended to accommodate massive partons. We
include the loop-induced contribution involving a Higgs coupling to a top
quark. We test our calculation against results existing in the literature,
comparing the predictions for the total decay width and jet rates.
