Crediting sources one has found citations from
The quoted you wrote is actually a pretty good way to include that citation.

It all comes down to the fundamental reason you are citing the paper. Citations are used to refer the reader to papers that contain useful information pertaining to your discussion. As such, “because it includes a good citation” is not a good reason for citing paper A in itself: there are plenty of other ways you could have found paper B (other citations, web or database search, bumping into its author at a meeting, etc.). Unless paper A adds relevant information to paper B, it should simply not be cited. One way it can add information is by performing a review of the literature, or by commenting on the results in paper B… In the first case, your quote is a good way to acknowledge that fact; in the second case, you could simply write that:


  Qwerty discussed in [21] the original results of Doe [22], showing how the data wasn't corrected to account for the phase of the moon at the time of measurement.


In conclusion, I'd say: determine whether paper A brings additional information, then either cite it or do not cite it. It is not common practice (and I don't think it should be) to acknowledge a paper without citing it.