Pending patent applications that comprise relevant prior art should be cited in a patent application or through the search process. But what about patent applications that got rejected? Should one still cite them?
If you decide to cite other patents within your application (which may or may not be a good idea), it doesn't matter what their status is. You do not cite them because they are patents or patent applications: you are citing them because they are prior art. An abandoned or rejected published patent application is as good prior art as a published patent.
If it is published, it is prior art (and as @DonQuiKong states, 'publishing' may be oral). If it is your own application that has not yet been publised (within deadline from filing or provisional filing) you may seek to amend the first application to keep its priority date or withdraw the first application to avoid publication and file a new one (with new priority date).