r0 = {xa, ya, za}

TableForm[
      mpa = {{Cos[alf], 0, -Sin[alf]}, {0, 1, 0}, {Sin[alf], 0, 
            Cos[alf]}}]

TableForm[
      mpb = {{1, 0, 0}, {0, Cos[bet], Sin[bet]}, {0, -Sin[bet], 
            Cos[bet]}}]

TableForm[r = mpb . mpa . r0]