I am going to assume that both the A-B output and the Siemens input are both 24VDC. If so, and, this is very important:
IF the A-B output card AND the Siemens input card receive power from the SAME power supply, you can connect the output wire from the sourcing output of the A-B PLC to the sinking input of the Siemens PLC. Since each I/O card is connected to the same power supply, the commons are connected locally at each card.
If the two I/O cards are NOT on the same 24VDC power supply, then you will need to use an interposing relay. The A-B output will be connected to the coil of the relay, and a NO contact on the relay will be connected to the Siemens digital input.