XBee Pro Rx pin 4V tolerant
The Digi Knowledge base is explicitly stating:


  To be clear, the inputs to the XBee module are NOT 5V tolerant and
  cannot accept a voltage level higher than 3.3v on any pin. Applying a
  voltage higher than 3.3V will damage the module and void your
  warranty. However, the following modules operate at 5V or are 5V
  tolerant: XCite, XStream, XTend, XBee XSC (S3 Only)