  Motivated by the recent experiment of the non-BCS scaling relation of the
condensation energy $\Delta CE$ vs. $T_c$ ($\Delta CE \sim T_c ^{\beta},
\beta\approx 3.5$) [PRB 89 140503 (2014)] for the Fe-based superconductors, we
studied the CE and $T_c$ of the multiband BCS superconductors. We showed that
the experimentally observed anomalous scaling relation $\Delta CE \sim T_c
^{3.5}$ is well reproduced by the two-band BCS superconductor paired by a
dominant interband interaction ($V_{inter} > V_{intra}$). Our result implies
that this seemingly non-BCS-like scaling behavior, on the contrary to the
common expectation, is in fact a strong experimental evidence that the pairing
mechanism of the Fe-based superconductors is genuinely a BCS mechanism, meaning
that "the Cooper pairs are formed by the itinerant carriers glued by a pairing
interaction."
