  We study the triangle mechanism for the decay $\tau^- \to \nu_\tau \pi^-
f_0(980)$, with the $f_0(980)$ decaying into $\pi^+ \pi^- $. This process is
initiated by $\tau^- \to \nu_\tau K^{*0} K^-$ followed by the $K^{*0}$ decay
into $\pi^- K^+$, then the $K^- K^+$ produce the $f_0(980)$ through a triangle
loop containing $ K^* K^+ K^-$ which develops a singularity around $1420$~MeV
in the $\pi f_0(980)$ invariant mass. We find a narrow peak in the $\pi^+
\pi^-$ invariant mass distribution, which originates from the $f_0(980)$
amplitude. Similarly, we also study the triangle mechanism for the decay $\tau
\to \nu \pi^- a_0(980)$, with the $a_0(980)$ decaying into $\pi^0 \eta $. The
final branching ratios for $\pi^- f_0(980)$ and $\pi^- a_0(980)$ are of the
order of $4 \times 10^{-4}$ and $7 \times 10^{-5}$, respectively, which are
within present measurable range. Experimental verification of these predictions
will shed light on the nature of the scalar mesons and on the origin for the
"$a_1(1420)$" peak observed in other reactions.
