how do you have to handle referencing/ citations in the following scenario:

In the first paragraph of a section, a concept A is introduced with a citation. In the following paragraph, another concept B is introduced.

Then in the third paragraph, both concepts are mentioned again (for example, to combine both to a concept C). Do you have to add a reference after both concepts again?

(1) "Combining concept A (Author S, date, p. XXX) and concept B (Author P, date, p. XX), a concept C supports the argument ..."

(2) "Combining concept A and concept B, ..."

Which approach is correct/ the best? If none, how shall this be done?