Mass of the $b$ Quark from QCD Sum Rules for $f_{B_{(s)}}$

We demonstrate that Borel QCD sum rules for heavy-light currents entail a very strong correlation between the $b$-quark mass $m_b$ and the $B$-meson decay constant $f_B,$ that is, $\delta f_B/f_B\approx-8\delta m_b/m_b.$ By starting from $f_B$ as input, this observation allows for an accurate sum-rule determination of $m_b.$ Employing precise lattice QCD results for $f_B$ in our sum-rule study based on the three-loop $O(\alpha_s^2)$ heavy-light correlation function implies $\bar{m}_b(\bar{m}_b)=(4.247\pm0.034)$ GeV for the $b$-quark $\bar{\rm MS}$ mass