  We have chosen the reactions $D_s^+ \to \pi^+ \pi^0 a_0(980) (f_0(980))$
investigating the isospin violating channel $D_s^+ \to \pi^+ \pi^0 f_0(980)$.
The reaction was chosen because by varying the $\pi^0 a_0(980) (f_0(980))$
invariant mass one goes through the peak of a triangle singularity emerging
from $D_s^+ \to \pi^+\bar K^* K$, followed by $\bar K^* \to \bar K \pi^0$ and
the further merging of $K \bar K$ to produce the $a_0(980)$ or $f_0(980)$. We
found that the amount of isospin violation had its peak precisely at the value
of the $\pi^0 a_0(980) (f_0(980))$ invariant mass where the singularity has its
maximum, stressing the role of the triangle singularities as a factor to
enhance the mixing of the $f_0(980)$ and $a_0(980)$ resonances. We calculate
absolute rates for the reactions and show that they are within present
measurable range. The measurement of these reactions would bring further
information into the role of triangle singularities in isospin violation and
the $a_0 -f_0$ mixing in particular and shed further light into the nature of
the low energy scalar mesons.
