I am looking for the earliest reference to the fact that any associative algebra becomes a Lie algebra with bracket $AXB-BXA$, where $X$ is a fixed element of the algebra. This is observed in the following paper:
Yanovski, A. B. "Linear bundles of Lie algebras and their applications." Journal of Mathematical Physics 41.11 (2000): 7869-7882.
But surely this is a much older result, at least for the case of matrix algebras.